Effect of D4 Dopamine Receptor on Na+-K+-ATPase Activity in Renal Proximal Tubule Cells.

Dopamine, via its receptors, plays a vital role in the maintenance of blood pressure by modulating renal sodium transport. However, the role of the D4 dopamine receptor (D4 receptor) in renal proximal tubules (PRTs) is still unclear. This study aimed to verify the hypothesis that activation of D4 receptor directly inhibits the activity of the Na+-K+-ATPase (NKA) in RPT cells. Methods: NKA activity, nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) levels were measured in RPT cells treated with the D4 receptor agonist PD168077 and/or the D4 receptor antagonist L745870, the NO synthase inhibitor NG-nitro-L-arginine-methyl ester (L-NAME) or the soluble guanylyl cyclase inhibitor 1H-[1,2,4] oxadiazolo-[4,3-a] quinoxalin-1-one (ODQ). Total D4 receptor expression and its expression in the plasma membrane were investigated by immunoblotting in RPT cells from Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs). Results: Activation of D4 receptors with PD168077, inhibited NKA activity in RPT cells from WKY rats in a concentration- and time-dependent manner. The inhibitory effect of PD168077 on NKA activity was prevented by the addition of the D4 receptor antagonist L745870, which by itself had no effect. The NO synthase inhibitor L-NAME and the soluble guanylyl cyclase inhibitor ODQ, which by themselves had no effect on NKA activity, eliminated the inhibitory effect of PD168077 on NKA activity. Activation of D4 receptors also increased NO levels in the culture medium and cGMP levels in RPT cells. However, the inhibitory effect of D4 receptors on NKA activity was absent in RPT cells from SHRs, which could be related to decreased plasma membrane expression of D4 receptors in SHR RPT cells. Conclusions: Activation of D4 receptors directly inhibits NKA activity via the NO/cGMP signaling pathway in RPT cells from WKY rats but not SHRs. Aberrant regulation of NKA activity in RPT cells may be involved in the pathogenesis of hypertension.

Muscle sodium content in patients with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome.

BACKGROUND: Muscle fatigue and pain are key symptoms of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS). Although the pathophysiology is not yet fully understood, there is ample evidence for hypoperfusion which may result in electrolyte imbalance and sodium overload in muscles. Therefore, the aim of this study was to assess levels of sodium content in muscles of patients with ME/CFS and to compare these to healthy controls. METHODS: Six female patients with ME/CFS and six age, BMI and sex matched controls underwent 23Na-MRI of the left lower leg using a clinical 3T MR scanner before and after 3 min of plantar flexion exercise. Sodium reference phantoms with solutions of 10, 20, 30 and 40 mmol/L NaCl were used for quantification. Muscle sodium content over 40 min was measured using a dedicated plugin in the open-source DICOM viewer Horos. Handgrip strength was measured and correlated with sodium content. RESULTS: Baseline tissue sodium content was higher in all 5 lower leg muscle compartments in ME/CFS compared to controls. Within the anterior extensor muscle compartment, the highest difference in baseline muscle sodium content between ME/CFS and controls was found (mean ± SD; 12.20 ± 1.66 mM in ME/CFS versus 9.38 ± 0.71 mM in controls, p = 0.0034). Directly after exercise, tissue sodium content increased in gastrocnemius and triceps surae muscles with + 30% in ME/CFS (p = 0.0005) and + 24% in controls (p = 0.0007) in the medial gastrocnemius muscle but not in the extensor muscles which were not exercised. Compared to baseline, the increase of sodium content in medial gastrocnemius muscle was stronger in ME/CFS than in controls with + 30% versus + 17% to baseline at 12 min (p = 0.0326) and + 29% versus + 16% to baseline at 15 min (p = 0.0265). Patients had reduced average handgrip strength which was associated with increased average muscle tissue sodium content (p = 0.0319, R2 = 0.3832). CONCLUSION: Muscle sodium content before and after exercise was higher in ME/CFS than in healthy controls. Furthermore, our findings indicate an inverse correlation between muscle sodium content and handgrip strength. These findings provide evidence that sodium overload may play a role in the pathophysiology of ME/CFS and may allow for potential therapeutic targeting.

Mild Hyperhomocysteinemia Causes Anxiety-like Behavior and Brain Hyperactivity in Rodents: Are ATPase and Excitotoxicity by NMDA Receptor Overstimulation Involved in this Effect?

Mild hyperhomocysteinemia is a risk factor for psychiatric and neurodegenerative diseases, whose mechanisms between them are not well-known. In the present study, we evaluated the emotional behavior and neurochemical pathways (ATPases, glutamate homeostasis, and cell viability) in amygdala and prefrontal cortex rats subjected to mild hyperhomocysteinemia (in vivo studies). The ex vivo effect of homocysteine on ATPases and redox status, as well as on NMDAR antagonism by MK-801 in same structures slices were also performed. Wistar male rats received a subcutaneous injection of 0.03 µmol Homocysteine/g of body weight or saline, twice a day from 30 to 60th-67th days of life. Hyperhomocysteinemia increased anxiety-like behavior and tended to alter locomotion/exploration of rats, whereas sucrose preference and forced swimming tests were not altered. Glutamate uptake was not changed, but the activities of glutamine synthetase and ATPases were increased. Cell viability was not altered. Ex vivo studies (slices) showed that homocysteine altered ATPases and redox status and that MK801, an NMDAR antagonist, protected amygdala (partially) and prefrontal cortex (totally) effects. Taken together, data showed that mild hyperhomocysteinemia impairs the emotional behavior, which may be associated with changes in ATPase and glutamate homeostasis, including glutamine synthetase and NMDAR overstimulation that could lead to excitotoxicity. These findings may be associated with the homocysteine risk factor on psychiatric disorders development and neurodegeneration.

Cytotoxic effect of carbohydrate derivatives of digitoxigenin involves modulation of plasma membrane Ca2+ -ATPase.

Cardiac glycosides, such as digoxin and digitoxin, are compounds that interact with Na+ /K+ -ATPase to induce anti-neoplastic effects; however, these cardiac glycosides have narrow therapeutic index. Thus, semi-synthetic analogs of digitoxin with modifications in the sugar moiety has been shown to be an interesting approach to obtain more selective and more effective analogs than the parent natural product. Therefore, the aim of this study was to assess the cytotoxic potential of novel digitoxigenin derivatives, digitoxigenin-α-L-rhamno-pyranoside (1) and digitoxigenin-α-L-amiceto-pyranoside (2), in cervical carcinoma cells (HeLa) and human diploid lung fibroblasts (Wi-26-VA4). In addition, we studied the anticancer mechanisms of action of these compounds by comparing its cytotoxic effects with the potential to modulate the activity of three P-type ATPases; Na+ /K+ -ATPase, sarco/endoplasmic reticulum Ca2+ -ATPase (SERCA), and plasma membrane Ca2+ -ATPase (PMCA). Briefly, the results showed that compounds 1 and 2 were more cytotoxic and selectivity for HeLa tumor cells than the nontumor cells Wi-26-VA4. While the anticancer cytotoxicity in HeLa cells involves the modulation of Na+ /K+ -ATPase, PMCA and SERCA, the modulation of these P-type ATPases was completely absent in Wi-26-VA4 cells, which suggest the importance of their role in the cytotoxic effect of compounds 1 and 2 in HeLa cells. Furthermore, the compound 2 inhibited directly erythrocyte ghosts PMCA and both compounds were more cytotoxic than digitoxin in HeLa cells. These results provide a better understanding of the mode of action of the synthetic cardiac glycosides and highlights 1 and 2 as potential anticancer agents.

Oxidant/antioxidant status in Type-2 diabetes mellitus patients with metabolic syndrome.

BACKGROUND: The concurrence of metabolic syndrome (MS) and diabetes mellitus (DM) is increasing worldwide. The long-term complications of these chronic diseases are a threat to patients' well-being. Oxidative stress is involved in the pathogenesis of several diseases. To understand the basic pathophysiological mechanisms of Type-2 DM (T2DM) and its related complications, we aimed to investigate the oxidant/antioxidant status and Na+-K+ ATPase activity in T2DM with MS. MATERIALS AND METHODS: A population of ninety individuals including fifty patients diagnosed with T2DM and MS, but without overt diabetes complications, and forty individuals without T2DM or MS as control group participated in this study. Plasma malondialdehyde (MDA), catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx) activities, total antioxidant capacity (TAC), and Na+-K+ ATPase activity were assessed by standard laboratory methods. RESULTS: Plasma MDA in patients group was statistically significantly higher than that of controls (P ≤ 0.05). Whereas, Na+-K+ ATPase activity was statistically significantly lower in patient group (P ≤ 0.05). TAC, CAT, SOD, and GPx enzyme activities were not statistically significantly different between two groups (P > 0.05). Results from the patient group showed positive correlations between CAT activity and triglyceride and positive correlations between GPx activity and weight, body mass index (BMI), and waist circumference. In addition, there was a positive correlation between MDA results with high-density lipoprotein-cholesterol (HDL-C) and total cholesterol and a negative correlation with TAC, BMI, and weight (P ≤ 0.05) in controls. CONCLUSION: Because T2DM patients were without any vascular complications, antioxidant defense results may reflect the lack of progression of diabetes complications in these patients. These results emphasize the need for initial and continued assessment of cardiovascular disease risks in diabetic individuals. Implementation of timely interventions may improve the management of diabetes and prevent the progression of diabetes complications.

Does Src Kinase Mediated Vasoconstriction Impair Penumbral Reperfusion?

Despite successful recanalization, a significant number of patients with ischemic stroke experience impaired local brain tissue reperfusion with adverse clinical outcome. The cause and mechanism of this multifactorial complication are yet to be understood. At the current moment, major attention is given to dysfunction in blood-brain barrier and capillary blood flow but contribution of exaggerated constriction of cerebral arterioles has also been suggested. In the brain, arterioles significantly contribute to vascular resistance and thus control of perfusion. Accordingly, pathological changes in arteriolar wall function can, therefore, limit sufficient reperfusion in ischemic stroke, but this has not yet received sufficient attention. Although an increased vascular tone after reperfusion has been demonstrated in several studies, the mechanism behind it remains to be characterized. Importantly, the majority of conventional mechanisms controlling vascular contraction failed to explain elevated cerebrovascular tone after reperfusion. We propose here that the Na,K-ATPase-dependent Src kinase activation are the key mechanisms responsible for elevation of cerebrovascular tone after reperfusion. The Na,K-ATPase, which is essential to control intracellular ion homeostasis, also executes numerous signaling functions. Under hypoxic conditions, the Na,K-ATPase is endocytosed from the membrane of vascular smooth muscle cells. This initiates the Src kinase signaling pathway that sensitizes the contractile machinery to intracellular Ca2+ resulting in hypercontractility of vascular smooth muscle cells and, thus, elevated cerebrovascular tone that can contribute to impaired reperfusion after stroke. This mechanism integrates with cerebral edema that was suggested to underlie impaired reperfusion and is further supported by several studies, which are discussed in this article. However, final demonstration of the molecular mechanism behind Src kinase-associated arteriolar hypercontractility in stroke remains to be done.

ATP1A3-Related Disorders: An Ever-Expanding Clinical Spectrum.

The Na+/K+ ATPases are Sodium-Potassium exchanging pumps, with a heteromeric α-ß-γ protein complex. The α3 isoform is required as a rescue pump, after repeated action potentials, with a distribution predominantly in neurons of the central nervous system. This isoform is encoded by the ATP1A3 gene. Pathogenic variants in this gene have been implicated in several phenotypes in the last decades. Carriers of pathogenic variants in this gene manifest neurological and non-neurological features in many combinations, usually with an acute onset and paroxysmal episodes triggered by fever or other factors. The first three syndromes described were: (1) rapid-onset dystonia parkinsonism; (2) alternating hemiplegia of childhood; and, (3) cerebellar ataxia, pes cavus, optic atrophy, and sensorineural hearing loss (CAPOS syndrome). Since their original description, an expanding number of cases presenting with atypical and overlapping features have been reported. Because of this, ATP1A3-disorders are now beginning to be viewed as a phenotypic continuum representing discrete expressions along a broadly heterogeneous clinical spectrum.

Targeting Cardiac Myocyte Na+-K+ Pump Function With ß3 Adrenergic Agonist in Rabbit Model of Severe Congestive Heart Failure.

BACKGROUND: Abnormally high cytosolic Na+ concentrations in advanced heart failure impair myocardial contractility. Stimulation of the membrane Na+-K+ pump should lower Na+ concentrations, and the ß3 adrenoceptor (ß3 AR) mediates pump stimulation in myocytes. We examined if ß3 AR-selective agonists given in vivo increase myocyte Na+-K+ pump activity and reverse organ congestion in severe heart failure (HF). METHODS: Indices for HF were lung-, heart-, and liver: body weight ratios and ascites after circumflex coronary artery ligation in rabbits. Na+-K+ pump current, Ip, was measured in voltage-clamped myocytes from noninfarct myocardium. Rabbits were treated with the ß3 AR agonists CL316,243 or ASP9531, starting 2 weeks after coronary ligation. RESULTS: Coronary ligation caused ascites in most rabbits, significantly increased lung-, heart-, and liver: body weight ratios, and decreased Ip relative to that for 10 sham-operated rabbits. Treatment with CL316,243 for 3 days significantly reduced lung-, heart-, and liver: body weight ratios and prevalence of ascites in 8 rabbits with HF relative to indices for 13 untreated rabbits with HF. It also increased Ip significantly to levels of myocytes from sham-operated rabbits. Treatment with ASP9531 for 14 days significantly reduced indices of organ congestion in 6 rabbits with HF relative to indices of 6 untreated rabbits, and it eliminated ascites. ß3 AR agonists did not significantly change heart rates or blood pressures. CONCLUSIONS: Parallel ß3 AR agonists-induced reversal of Na+-K+ pump inhibition and indices of congestion suggest pump inhibition is a useful target for treatment with ß3 AR agonists in congestive HF.

Association between a novel G94A single nucleotide polymorphism in ATP1A1 gene and type 2 diabetes mellitus among Egyptian patients.

BACKGROUND: Na+/K+ ATPase enzyme is essential for nerve cell membrane integrity, and reduction in its activity, probably due to ATP1A1 gene polymorphisms, is related to diabetic neuropathy progression. Therefore, the goal of the existent study is to evaluate the Na+/K+ ATPase activity in type 2 diabetes mellitus (T2DM) Egyptian patients with or without neuropathy, search for polymorphism(s) in the highly polymorphic region of ATP1A1 gene, exon 2, and study its (their) associations with T2DM with and without neuropathy. MATERIALS AND METHODS: A total number of 150 individuals were subclassified into healthy controls (n = 30), T2DM without complications (n = 60), and T2DM with neuropathy (n = 60). RESULTS: The biochemical results exhibited a significant reduction in fasting C-Peptide and activity of Na+/K+ ATPase in T2DM patients with neuropathy followed by T2DM without complication in comparison with healthy controls. ATP1A1 exon2 was amplified by polymerase chain reaction (PCR) then digested by the PstI restriction enzyme, and the obtained data from restriction fragment length polymorphism-PCR and sequencing revealed the existence of a novel synonymous G94A single nucleotide polymorphism (SNP) at nucleotide 27 in exon 2 of ATP1A1 gene (rs1060366). Diabetic groups had only allele A, while the control group had G allele. Interestingly, individuals carrying AA genotype had a significantly lower Na+/K+ ATPase, C-peptide, and higher glycosylated hemoglobin (HBA1c %) than those having GG genotype, suggesting a possible association for this SNP, and this developed phenomenon of not only T2DM but also diabetic neuropathy. CONCLUSION: Thus, allele A of G94A SNP (rs1060366) could be a risk allele for diabetes susceptibility among Egyptian patients.

[Phenotypic and genotypic characteristics of fever-induced paroxysmal weakness and encephalopathy caused by ATP1A3 pathogenic variants].

Objective: To characterize fever-induced paroxysmal weakness and encephalopathy (FIPWE) caused by ATP1A3 gene pathogenic variant. Methods: Phenotypic and genotypic characteristics of 4 FIPWE patients (3 boys and 1 girl), who were ascertained from October 2016 to March 2018 in Beijing Children's Hospital due to ATP1A3 heterozygous variants, were retrospectively analyzed. The whole exsome sequencing was used for genetic testing. Results: The onset ages of 4 patients were 2 years and 9 months, 2 years and 4 months, 8 months, 2 years and 5 months respectively. The episode ranged from 1 to 3 times, and at 3 months to 2 years and 10 months intervals. All 4 patients had symptoms of limb weakness and encephalopathy, accompanied with mild to severe ataxia or athetosis. The tendon reflex was absent in all patients, and the Babinski's sign was positive. Three patients had dysphagia and 3 patients had slurred speech. Three patients had abnormal eye movements, including strabismus and opsoclonus. None of the 4 patients exhibited visual impairment, auditory impairment or talipes cavus. The duration of acute phase ranged from 1 week to 3 months. In 3 relapsing patients, symptoms became progressively worse, with relapses occurring frequently and recovery being more difficult, and various sequelae were found after the last relapse. All patients carried heterozygous variant in ATP1A3 gene. The missense variants result in the substitution of an arginine residue at position 756. Three variants were identified, including C. 2267G > T (p. R756L) (1 case), C. 2266C > T (p. R756C) (2 cases), and C. 2267G > A (p. R756H) (1 case). Three were de novo and one inherited from his father, but the grandparents did not carry the variant. All variants were reported as pathogenic. Conclusions: FIPWE is one of new clinical phenotypes of ATP1A3 spectrum disease and most cases are sporadic. The missense variants result in the substitution of an arginine residue at position 756. This report provided insights into the phenotype-genotype association in patients with FIPWE caused by pathogenic variants of ATP1A3.

Phenotypic and genotypic characteristics of fever-induced paroxysmal weakness and encephalopathy caused by ATP1A3 pathogenic variants / 中华儿科杂志

Objective@#To characterize fever-induced paroxysmal weakness and encephalopathy (FIPWE) caused by ATP1A3 gene pathogenic variant.@*Methods@#Phenotypic and genotypic characteristics of 4 FIPWE patients (3 boys and 1 girl), who were ascertained from October 2016 to March 2018 in Beijing Children's Hospital due to ATP1A3 heterozygous variants, were retrospectively analyzed. The whole exsome sequencing was used for genetic testing.@*Results@#The onset ages of 4 patients were 2 years and 9 months, 2 years and 4 months, 8 months, 2 years and 5 months respectively. The episode ranged from 1 to 3 times, and at 3 months to 2 years and 10 months intervals. All 4 patients had symptoms of limb weakness and encephalopathy, accompanied with mild to severe ataxia or athetosis. The tendon reflex was absent in all patients, and the Babinski's sign was positive. Three patients had dysphagia and 3 patients had slurred speech. Three patients had abnormal eye movements, including strabismus and opsoclonus. None of the 4 patients exhibited visual impairment, auditory impairment or talipes cavus. The duration of acute phase ranged from 1 week to 3 months. In 3 relapsing patients, symptoms became progressively worse, with relapses occurring frequently and recovery being more difficult, and various sequelae were found after the last relapse. All patients carried heterozygous variant in ATP1A3 gene. The missense variants result in the substitution of an arginine residue at position 756. Three variants were identified, including C. 2267G > T (p. R756L) (1 case), C. 2266C > T (p. R756C) (2 cases), and C. 2267G > A (p. R756H) (1 case). Three were de novo and one inherited from his father, but the grandparents did not carry the variant. All variants were reported as pathogenic.@*Conclusions@#FIPWE is one of new clinical phenotypes of ATP1A3 spectrum disease and most cases are sporadic. The missense variants result in the substitution of an arginine residue at position 756. This report provided insights into the phenotype-genotype association in patients with FIPWE caused by pathogenic variants of ATP1A3.

Expression of NKCC1 and Na-K-ATPase in C57BL/6J mice with age-related hearing loss / 中国耳鼻咽喉头颈外科

OBJECTIVE Disturbance of K+ ion balance in inner ear is associated in age-related hearing loss. Our study is to investigate the role of NKCC1 and Na-K-ATPase in cochlea and auditory function regulated by with different expression of NKCC1 and Na-K-ATPase. METHODS Auditory threshold of young or old C57BL/6J mice was measured by auditory brainstem response(ABR). The expression of NKCC1 and Na-K-ATPase in mice cochlea were evaluated by reverse transcription polymerase chain reaction(RT-PCR) and western blotting. Furosemide and Ouabain were applied in vivo to inhibit NKCC1 and Na-K-ATPase in C57BL/6J mice. RESULTS C57BL/6J mice developed hearing loss at 12M by ABR threshold shifting to (75±10), (78±26) and (81±14)dB SPL at frequencies of 8, 16 and 32 kHz; PCR showed that the relative expression of NKCC1 and Na-K-ATPase mRNA in the aged group decreased, which were 0.52±0.06 and 0.35±0.04 times higher than those in the young control group, the difference was statistically significant(t =7.466 and 16.11, all P＜0.05). WB showed that relative expression of NKCC1 and Na-K-ATPase protein level in the aged group decreased by 0.79±0.02 and 0.68±0.05 times as much as that of the young control group, the difference was statistically significant(t =8.857 and 6.771, P all＜0.05). After applied with Furosemide and Ouabain to suppress the two ion transporters, the ABR threshold increased to (50±17), (53±21), (55±17)dB SPL and (56±6), (70±17), (73±6)dB SPL at frequencies of 8, 16 and 32 kHz. CONCLUSION In vivo experiment of C57BL/6J suggested that NKCC1 and Na-K-ATPase might be related to age related hearing loss.

The Slow Dynamics of Intracellular Sodium Concentration Increase the Time Window of Neuronal Integration: A Simulation Study.

Changes in intracellular Na+ concentration ([Na+]i) are rarely taken into account when neuronal activity is examined. As opposed to Ca2+, [Na+]i dynamics are strongly affected by longitudinal diffusion, and therefore they are governed by the morphological structure of the neurons, in addition to the localization of influx and efflux mechanisms. Here, we examined [Na+]i dynamics and their effects on neuronal computation in three multi-compartmental neuronal models, representing three distinct cell types: accessory olfactory bulb (AOB) mitral cells, cortical layer V pyramidal cells, and cerebellar Purkinje cells. We added [Na+]i as a state variable to these models, and allowed it to modulate the Na+ Nernst potential, the Na+-K+ pump current, and the Na+-Ca2+ exchanger rate. Our results indicate that in most cases [Na+]i dynamics are significantly slower than [Ca2+]i dynamics, and thus may exert a prolonged influence on neuronal computation in a neuronal type specific manner. We show that [Na+]i dynamics affect neuronal activity via three main processes: reduction of EPSP amplitude in repeatedly active synapses due to reduction of the Na+ Nernst potential; activity-dependent hyperpolarization due to increased activity of the Na+-K+ pump; specific tagging of active synapses by extended Ca2+ elevation, intensified by concurrent back-propagating action potentials or complex spikes. Thus, we conclude that [Na+]i dynamics should be considered whenever synaptic plasticity, extensive synaptic input, or bursting activity are examined.

The Effects of Altered Membrane Cholesterol Levels on Sodium Pump Activity in Subclinical Hypothyroidism.

BACKGROUND: Metabolic dysfunctions characteristic of overt hypothyroidism (OH) start at the early stage of subclinical hypothyroidism (SCH). Na⁺/K⁺-ATPase (the sodium pump) is a transmembrane enzyme that plays a vital role in cellular activities in combination with membrane lipids. We evaluated the effects of early changes in thyroid hormone and membrane cholesterol on sodium pump activity in SCH and OH patients. METHODS: In 32 SCH patients, 35 OH patients, and 34 euthyroid patients, sodium pump activity and cholesterol levels in red blood cell membranes were measured. Serum thyroxine (T4) and thyroid stimulating hormone (TSH) levels were measured using enzyme-linked immunosorbent assays. Differences in their mean values were analysed using post hoc analysis of variance. We assessed the dependence of the sodium pump on other metabolites by multiple regression analysis. RESULTS: Sodium pump activity and membrane cholesterol were lower in both hypothyroid groups than in control group, OH group exhibiting lower values than SCH group. In SCH group, sodium pump activity showed a significant direct dependence on membrane cholesterol with an inverse relationship with serum TSH levels. In OH group, sodium pump activity depended directly on membrane cholesterol and serum T4 levels. No dependence on serum cholesterol was observed in either case. CONCLUSION: Despite the presence of elevated serum cholesterol in hypothyroidism, membrane cholesterol contributed significantly to maintain sodium pump activity in the cells. A critical reduction in membrane cholesterol levels heralds compromised enzyme activity, even in the early stage of hypothyroidism, and this can be predicted by elevated TSH levels alone, without any evident clinical manifestations.

Effect of sevoflurane on activities of Na+-K+-ATPase and Ca2+-ATPase in hippocampus of diabetic rats / 中华麻醉学杂志

Objective To evaluate the effect of sevoflurane on activities of Na+-K+-ATPase and Ca2+-ATPase in the hippocampus of diabetic rats.Methods SPF healthy male Wistar rats,aged 8 weeks,weighing 180-200 g,were fed a high-fat diet for 3 consecutive weeks and streptozotocin was intraperitoneal-ly injected to induce type 2 diabetes mellitus.Forty-four rats with diabetes mellitus were divided into 2 groups (n=22 each) using a random number table:diabetic group (D group) and sevoflurane group (S group).Another 22 healthy Wistar rats,aged 8 weeks,weighing 180-200 g,served as control group (C group).Oxygen was inhaled for 2 h in C and D groups,and 2.4％ sevoflurane was inhaled for 2 h in S group.Eight rats were sacrificed at 30 min after treatment,brains were removed and hippocampi were isolated for measurement of Na+-K+-ATPase and Ca2+-ATPase activities in hippocampal tissues by spectrophotometry.Ten rats were randomly selected at 1 day after treatment,and Morris water maze test was performed to assess the cognitive function.Four rats were randomly sacrificed,brains were removed and hippocampi were isolated for examination of the mitochondrial ultrastructure with a transmission electron microscope.Results Compared with group C,the escape latency was significantly prolonged,the number of crossing the original platform was reduced,the percentage of time of staying at the original platform quadrant was decreased,the activities of Na+-K+-ATPase and Ca2+-ATPase in hippocampi were decreased (P＜ 0.05),and mitochondrial swelling and decreased mitochondrial cristae were observed under the electron microscope in group D.Compared with group D,the escape latency was significantly prolonged,the number of crossing the original platform was reduced,the percentage of time of staying at the original platform quadrant was decreased,the activities of Na+-K+-ATPase and Ca2+-ATPase in hippocampi were decreased (P＜ 0.05),and mitochondrial swelling and vacuolization were found under the electron microscope in group S.Conclusion The mechanism by which sevoflurane aggravates cognitive dysfunction is related to deceasing activities of Na+-K+-ATPase and Ca2+-ATPase in the hippocampus of diabetic rats.

The Effects of Altered Membrane Cholesterol Levels on Sodium Pump Activity in Subclinical Hypothyroidism

BACKGROUND: Metabolic dysfunctions characteristic of overt hypothyroidism (OH) start at the early stage of subclinical hypothyroidism (SCH). Na⁺/K⁺-ATPase (the sodium pump) is a transmembrane enzyme that plays a vital role in cellular activities in combination with membrane lipids. We evaluated the effects of early changes in thyroid hormone and membrane cholesterol on sodium pump activity in SCH and OH patients. METHODS: In 32 SCH patients, 35 OH patients, and 34 euthyroid patients, sodium pump activity and cholesterol levels in red blood cell membranes were measured. Serum thyroxine (T₄) and thyroid stimulating hormone (TSH) levels were measured using enzyme-linked immunosorbent assays. Differences in their mean values were analysed using post hoc analysis of variance. We assessed the dependence of the sodium pump on other metabolites by multiple regression analysis. RESULTS: Sodium pump activity and membrane cholesterol were lower in both hypothyroid groups than in control group, OH group exhibiting lower values than SCH group. In SCH group, sodium pump activity showed a significant direct dependence on membrane cholesterol with an inverse relationship with serum TSH levels. In OH group, sodium pump activity depended directly on membrane cholesterol and serum T4 levels. No dependence on serum cholesterol was observed in either case. CONCLUSION: Despite the presence of elevated serum cholesterol in hypothyroidism, membrane cholesterol contributed significantly to maintain sodium pump activity in the cells. A critical reduction in membrane cholesterol levels heralds compromised enzyme activity, even in the early stage of hypothyroidism, and this can be predicted by elevated TSH levels alone, without any evident clinical manifestations.

"Oxygen Sensing" by Na,K-ATPase: These Miraculous Thiols.

Control over the Na,K-ATPase function plays a central role in adaptation of the organisms to hypoxic and anoxic conditions. As the enzyme itself does not possess O2 binding sites its "oxygen-sensitivity" is mediated by a variety of redox-sensitive modifications including S-glutathionylation, S-nitrosylation, and redox-sensitive phosphorylation. This is an overview of the current knowledge on the plethora of molecular mechanisms tuning the activity of the ATP-consuming Na,K-ATPase to the cellular metabolic activity. Recent findings suggest that oxygen-derived free radicals and H2O2, NO, and oxidized glutathione are the signaling messengers that make the Na,K-ATPase "oxygen-sensitive." This very ancient signaling pathway targeting thiols of all three subunits of the Na,K-ATPase as well as redox-sensitive kinases sustains the enzyme activity at the "optimal" level avoiding terminal ATP depletion and maintaining the transmembrane ion gradients in cells of anoxia-tolerant species. We acknowledge the complexity of the underlying processes as we characterize the sources of reactive oxygen and nitrogen species production in hypoxic cells, and identify their targets, the reactive thiol groups which, upon modification, impact the enzyme activity. Structured accordingly, this review presents a summary on (i) the sources of free radical production in hypoxic cells, (ii) localization of regulatory thiols within the Na,K-ATPase and the role reversible thiol modifications play in responses of the enzyme to a variety of stimuli (hypoxia, receptors' activation) (iii) redox-sensitive regulatory phosphorylation, and (iv) the role of fine modulation of the Na,K-ATPase function in survival success under hypoxic conditions. The co-authors attempted to cover all the contradictions and standing hypotheses in the field and propose the possible future developments in this dynamic area of research, the importance of which is hard to overestimate. Better understanding of the processes underlying successful adaptation strategies will make it possible to harness them and use for treatment of patients with stroke and myocardial infarction, sleep apnoea and high altitude pulmonary oedema, and those undergoing surgical interventions associated with the interruption of blood perfusion.

Possible senescence associated change in the predominant a-Na+/K+ ATP-ase isoform in the renal cortex of the rat.

With aging the kidney exhibits progressive deterioration, with a decrease in renal function. Most of the filtered Na+ is actively reabsorbed in the proximal tubules through different transporters located in apical membrane. This process is possible because basolateral Na+/K+-ATP-ase generates electrochemical conditions necessary for energetically favorable Na+ transport. The a-subunit is the catalytic domain of Na+/K+-ATP-ase. There are three isoforms of the a/subunit present in rat kidney. The present study was undertaken to examine the expression pattern of rat a-Na+/K+-ATP-ase during senescence. We tested the impact of aging on mRNA expression of a-Na+/K+-ATP-ase in cortex and medulla of aged Wistar rats. We observed a significant expression decrease in mRNA levels and a possible change of isoform in the cortex of aged animals. These expression changes observed for a subunit could be contributing to affect the renal function in conditions of water and salt stress.

Possible senescence associated change in the predominant &alpha -Na+/K+ ATP-ase isoform in the renal cortex of the rat

With aging the kidney exhibits progressive deterioration, with a decrease in renal function. Most of the filtered Na+ is actively reabsorbed in the proximal tubules through different transporters located in apical membrane. This process is possible because basolateral Na+/K+-ATP-ase generates electrochemical conditions necessary for energetically favorable Na+ transport. The α-subunit is the catalytic domain of Na+/K+-ATP-ase. There are three isoforms of the α/subunit present in rat kidney. The present study was undertaken to examine the expression pattern of rat α-Na+/K+-ATP-ase during senescence. We tested the impact of aging on mRNA expression of α-Na+/K+-ATP-ase in cortex and medulla of aged Wistar rats. We observed a significant expression decrease in mRNA levels and a possible change of isoform in the cortex of aged animals. These expression changes observed for αsubunit could be contributing to affect the renal function in conditions of water and salt stress.

Con el avance de la edad los riñones exhiben un deterioro funcional progresivo con disminución de la función renal. La mayor parte del sodio (Na+) filtrado es reabsorbido activamente en los túbulos proximales a través de diferentes transportadores ubicados en la membrana apical. Este proceso es posible por la existencia de la Na+/K+-ATP-asa basolateral, que genera las condiciones electroquímicas necesarias para que el transporte de Na+ sea energéticamente favorable. La subunidad αde la Na+/K+-ATP-asa es el dominio catalítico de la enzima. Existen tres isoformas de subunidad α, que están presentes en el riñón de la rata. En este trabajo se examinan los patrones de expresión de la α-Na+/K+-ATP-asa durante la senescencia. Se estudió así si el aumento de la edad incidía en la expresión del ARNm de la α-Na+/K+-ATP-asa en corteza y médula renal de ratas Wistar senescentes. Se observó una disminución en la expresión del ARNm de la subunidad αy un posible cambio de isoforma predominante en la corteza de los animales senescentes. Los cambios observados para la expresión de la subunidad αpodrían contribuir a afectar la función renal en condiciones de estrés hídrico y salino.

Aspectos clínicos, fisiopatológicos e genéticos das tubulopatias hereditárias na infância / Clinical, pathophysiological and genetic aspects of inherited tubular disorders in childhood

ResumoNesta revisão, descrevemos a função tubular de cada segmento do néfron seguida das descrições das principais alterações moleculares que possam ocorrer nos transportadores expressos nestes locais. Assim, o conhecimento das modificações na função tubular renal permite o entendimento e o reconhecimento clínico das doenças tubulares renais que podem causar a morte fetal, neonatal ou infantil. Além disso, as crianças com tubulopatias podem evoluir para doença renal crônica terminal numa fase precoce da vida e também podem apresentar distúrbios do crescimento e do desenvolvimento acompanhados ou não de alterações neurológicas. Então, nós utilizamos o unitermo "inherited tubular disorders" a fim de selecionar na base de dados do PubMed os estudos publicados desde 2006. Esperamos que a leitura desta revisão auxilie no rápido diagnóstico dos pacientes com tubulopatias, o que poderá permitir o tratamento especializado e a possível melhora do prognóstico e qualidade de vida destes indivíduos.

AbstractIn this review, we described the tubular function of each nephron segment followed by the most important changes that may occur in the transporters expressed therein. Thus, knowledge of the changes in renal tubular function allows the understanding and recognition of renal tubular diseases that can cause stillbirth or death in newborns or in childhood. Moreover, children with tubular disorders may progress to chronic renal disease at an early stage of life and they may also show disturbances of growth and development associate or not with neurological dysfunction. Therefore, we used the keyword "inherited tubular disorders" to select the children studies that have been published in the PubMed database since 2006. We hope that this review may help physicians to perform an early diagnosis in patients with tubular disorders allowing a specialized treatment and an improvement in their prognosis and quality of life.