Transportadores de iones en pulmón: Uso como dianas terapéuticas / Ion transporters in the lungs. Use as therapeutic targets

Los canales de cloruros, de sodio, de bicarbonato y los de agua (aquaporinas) se coordinan para mantener la cubierta líquido superficial de las vías respiratorias, que es necesaria para el aclaramiento mucociliar. El mecanismo general para el transporte de electrolitos y agua depende principalmente de la expresión diferencial y distribución de los transportadores y bombas de iones. Los iones y el agua se mueven a través de las vía paracelular o transcelular. La ruta transcelular del transporte de electrolitos requiere un transporte activo (dependiente de ATP) o pasivo (siguiendo gradientes electroquímicos) de iones. La ruta paracelular es un proceso pasivo que está controlado, en última instancia, por los gradientes electroquímicos transepiteliales predominantes. La fibrosis quística es una enfermedad hereditaria que se produce por mutaciones en el gen que codifica la proteína reguladora de la conductibilidad transmembrana de la fibrosis quística (CFTR) que actúa como un canal de cloro y cumple funciones de hidratación del líquido periciliar y mantenimiento del pH luminal. La disfunción del canal de cloro en el epitelio respiratorio determina una alteración en las secreciones bronquiales, con aumento de su viscosidad y alteración de la depuración mucociliar y que asociado a procesos infecciosos puede conducir a daño pulmonar irreversible. La disfunción del CFTR, también se ha visto implicado en la patogénesis de la pancreatitis aguda, en la enfermedad pulmonar obstructiva crónica y la hiperreactividad en el asma. Existen fármacos que aprovechan los mecanismos fisiológicos en el transporte de iones, con un objetivo terapéutico.

The chloride channels, sodium and bicarbonate channels, and aquaporin water channels are coordinated to maintain the airway surface liquid that is necessary for mucociliary clearance. The general mechanism for the transport of electrolytes and fluids depends mainly on the differential expression and distribution of ion transporters and pumps. Ions and water move through the paracellular or transcellular pathways. The transcellular route of electrolyte transport requires an active transport (dependent on ATP) or passive (following electrochemical gradients) of ions. The paracellular pathway is a passive process that is ultimately controlled by the predominant transepithelial electrochemical gradients. Cystic fibrosis is a hereditary disease that is produced by mutations in the gene that encode cystic fibrosis transmembrane conductance regulatory protein (CFTR) that acts as a chloride channel and performs functions of hydration of periciliary fluid and maintenance of luminal pH. The dysfunction of the chlorine channel in the respiratory epithelium determines an alteration in the bronchial secretions, with an increase in its viscosity and alteration of the mucociliary clearance and that associated with infectious processes can lead to irreversible lung damage. CFTR dysfunction has also been implicated in the pathogenesis of acute pancreatitis, chronic obstructive pulmonary disease, and bronchial hyperreactivity in asthma. There are drugs that exploit physiological mechanisms in the transport of ions with a therapeutic objective.

Impact of acute undernutrition on growth, ileal morphology and nutrient transport in a murine model

Undernutrition represents a major public health challenge for middle- and low-income countries. This study aimed to evaluate whether a multideficient Northeast Brazil regional basic diet (RBD) induces acute morphological and functional changes in the ileum of mice. Swiss mice (∼25 g) were allocated into two groups: i) control mice were fed a standard diet and II) undernourished mice were fed the RBD. After 7 days, mice were killed and the ileum collected for evaluation of electrophysiological parameters (Ussing chambers), transcription (RT-qPCR) and protein expression (western blotting) of intestinal transporters and tight junctions. Body weight gain was significantly decreased in the undernourished group, which also showed decreased crypt depth but no alterations in villus height. Electrophysiology measurements showed a reduced basal short circuit current (Isc) in the undernourished group, with no differences in transepithelial resistance. Specific substrate-evoked Isc related to affinity and efficacy (glutamine and alanyl-glutamine) were not different between groups, except for the maximum Isc (efficacy) induced by glucose. Transcription of Sglt1 and Pept1 was significantly higher in the undernourished group, while SN-2 transcription was decreased. No changes were found in transcription of CAT-1 and CFTR, while claudin-2 and occludin transcriptions were significantly increased in the undernourished group. Despite mRNA changes, SGLT-1, PEPT-1, claudin-2 and occludin protein expression showed no difference between groups. These results demonstrate early effects of the RBD on mice, which include reduced body weight and crypt depth in the absence of significant alterations to villus morphology, intestinal transporters and tight junction expression.

Expression studies on NA+/K+-ATPase in gills of Penaeus monodon (Fabricius) acclimated to different salinities.

The decapod crustacean Penaeus monodon survives large fluctuations in salinity through osmoregulation in which Na+/K+-ATPase (NKA) activity in the gills plays a central role. Adult P. monodon specimens were gradually acclimatized to 5, 25 and 35‰ salinities and maintained for 20 days to observe long term alterations in NKA expression. Specific NKA activity assayed in gill tissues was found to be 3 folds higher at 5‰ compared to 25‰ (isosmotic salinity) and 0.48 folds lower at 35‰. The enzyme was immunolocalized in gills using mouse α-5 monoclonal antibody that cross reacts with P. monodon NKA α-subunit. At 5‰ the immunopositive cells were distributed on lamellar tips and basal lamellar epithelium of the secondary gill filaments and their number was visibly higher. At both 25‰ and 35‰ NKA positive cells were observed in the inter-lamellar region but the expression was more pronounced at 25‰. Gill architecture was normal at all salinities. However, the 1.5 fold increase in NKA α-subunit mRNA at 5‰ measured by quantitative RT-PCR (qRT-PCR) using EF1α as reference gene was not statistically significant. The study confirms the osmoregulating ability of P. monodon like other crustaceans at lower salinities. It is likely that significant increase in NKA transcript level happens at an earlier time point. At higher salinities all three methods record only marginal or no change from isosmotic controls confirming the hypothesis that the animal largely osmoconforms in hyperosmotic environment.

Effects of low intensity electromagnetic irradiation of 70.6 and 73 GHz frequencies and antibiotics on energy-dependent proton and potassium ion transport by E. coli.

The effects of low intensity (flux capacity 0.06 mW/cm2) coherent electromagnetic irradiation (EMI) of 70.6 and 73 GHz frequencies and their combined effects with antibiotics — ceftriaxone or kanamycin (0.4 or 15 µM, correspondingly) on E. coli K12 growth and survival have been reported previously. To further study the effects of EMI and antibiotics and mechanisms, decrease in overall energy (glucose)-dependent H+ and K+ fluxes across the cell membrane was investigated in E. coli. The depression of H+ and K+ fluxes rate was maximally achieved with the 73 GHz frequency. The EMI strengthened the effect of N,N’-dicyclohexycarbodiimide (DCCD, an inhibitor of the F0F1-ATPase). The 73 GHz EMI had more influence on H+ efflux inhibition, whereas 70.6 GHz on K+ influx. Also, EMI strengthened the depressive effects of ceftriaxone and kanamycin on the overall and DCCD-inhibited H+ and K+ fluxes. The 73 GHz EMI strengthened the effect of ceftriaxone on both ions fluxes. Kanamycin depressed H+ efflux more as compared to ceftriaxone, which was also strengthened with EMI. The results of E. coli H+ and K+ transport systems activities depression by irradiation and the irradiation effect on DCCD and antibiotics action indicated the EMI and antibiotics causing primary changes in the bacterial membrane.

Rhodnius prolixus Malpighian tubules and control of diuresis by neurohormones

Rhodnius prolixus Malpighian tubules (MTs) are a good model for fluid and ion secretion studies in view of the dramatic postprandial diuresis, which follows its massive blood meals. Ingestion of a blood meal equals to 10-12 times their initial body mass, leads to rapid activation of high output by excretory system, which eliminates 40-50 percent of the fluid mass. Secretion of ions and water is stimulated 1000-fold by serotonin and diuretic hormone. These hormones cooperate synergistically to activate adenylate cyclase activity from MTs cells, which increase the level of intracellular cAMP. The anti-diuretic hormones have also an important role in the fluid maintenance of Rhodnius prolixus. Several hours after insect feeding occurs a reduction in urine flow, that has been thought to result from a decreased diuretic hormone release or from a novel mechanism of anti-diuresis involving insect cardioacceleratory peptide 2b (CAP2b) and cyclic GMP. In this article it is discussed how the hormone regulation of fluid transport is done in Rhodnius prolixus MTs.

Os túbulos de Malpighi (TMs) de Rhodnius prolixus são reconhecidos por serem excelentes modelos para o estudo da secreção de fluidos e íons devido a grande diurese que ocorre quando esses animais se alimentam de sangue. O inseto, após alimentação, pode aumentar seu peso corporal inicial em até 10-12 vezes, o que leva a rápida ativação do sistema excretor, que elimina 40-50 por cento do fluido corporal. A secreção de íons e água é estimulada 1000 vezes pela serotonina e pelos hormônios diuréticos. Esses hormônios agem sinergicamente ativando a adenil ciclase das células dos TMs, aumentando os níveis intracelulares de AMPc. Os hormônios anti-diuréticos também têm um importante papel na manutenção dos fluídos corporais do Rhodnius prolixus. Várias horas após a alimentação do inseto ocorre uma redução do fluxo urinário, o que foi sugerido ser decorrente da diminuição da liberação dos hormônios diuréticos ou da anti-diurese envolvendo o peptídeo cardioaceleratório 2b (CAP2b) e o GMPc. Neste artigo é discutida a regulação hormonal do transporte de fluido nos MTs de Rhodnius prolixus.

pH-dependent modulation of intracellular free magnesium ions with ionselective electrodes in papillary muscle of guinea pig

A change in pH can alter the intracellular concentration of electrolytes such as intracellular Ca2+ and Na+ ([Na+]i) that are important for the cardiac function. For the determination of the role of pH in the cardiac magnesium homeostasis, the intracellular Mg2+ concentration ([Mg2+]i), membrane potential and contraction in the papillary muscle of guinea pigs using ion-selective electrodes changing extracellular pH ([pH]o) or intracellular pH ([pH]i) were measured in this study. A high CO2-induced low [pH]o causes a significant increase in the [Mg2+]i and [Na+]i, which was accompanied by a decrease in the membrane potential and twitch force. The high [pH]o had the opposite effect. These effects were reversible in both the beating and quiescent muscles. The low [pH]o-induced increase in [Mg2+]i occurred in the absence of [Mg2+]o. The [Mg2+]i was increased by the low [pH]i induced by propionate. The [Mg2+]i was increased by the low [pH]i induced by NH4Cl-prepulse and decreased by the recovery of [pH]i induced by the removal of NH4Cl. These results suggest that the pH can modulate [Mg2+]i with a reverse relationship in heart, probably by affecting the intracellular Mg2+ homeostasis, but not by Mg2+ transport across the sarcolemma.

Human red blood cells from prenatal hemopoiesis. Lithium flux (sodium dependent) asymmetry

In red cells from umbilical cord blood it has been referred the existence of lithium fluxes (contralateral sodium dependent) asymmetry. On account of the relevancy of this transport system in some pathologies it is pertinent the study of its kinetics to relate normal with pathological states in which it is affected. Lithium fluxes--contralateral sodium dependent were determined in N-ethylmaleimide treated neonatal red blood cells. Experimental data were fitted by simple Michaelis-Menten kinetics, finding Km and Vmax variables. It was shown the persistency of asymmetry. The independence of sulfhydryl groups (or the occultation of the groups involved to this inhibitor) could explain asymmetry persistence.

Nutrition-physiology link: need to increase basic research

Comentam-se alguns mecanismos complexos da absorçäo intestinal em relaçäo ao seu elo com interaçöes entre nutrientes, ou ao sistema alimentar, em si. Considera-se também a biodisponibilidade de nutrientes em relaçäo ao estado nutricional dos indivíduos, afim de enfatizar a necessidade de maior conhecimento da fisiologia para a melhor compreensäo da nutriçäo, e vice-versa

Effect of HCO3 and pH on ion transport in the posterior intestine of the freshwater-adapted teleost Anguilla anguilla

The intestinal mucosa may be exposed to acidic or alcaline solutions due to liberation of digestive secretions. In several situations blood pH may also change. Consequently, the effects of HCO-3, CO2, and pH variation of medium on the ion transport acrross the posterior intestine of the eel (Anguilla anguilla) adapted to freshwater were studied in terms of fractional values of short-circuit current (SCC), transepithelial potential difference (TPD) and conductance (G). Immature eels weighing 100-200 g were used. The control physiological solution contained: 118.5 mM NaCl, 25.0 mM NaHCO3, 3.0 mM CaCl2.2H2O, 4.7 mM KCl, 1.0 mM MgCl2.6H2O, 5.0 mMD-glucose, 10.0 mM D-mannitol, pH 7.80, and was gassed with 98 percent O2-2 percent CO2. Control values(N = 21) were: SCC = 51.90 + or - 51.90 + or - 2.8 µA.cm-2, TPD = 2.33 + or - 0.1 mV, G = 22.43 + or - 0.6 mS.cm-2. At constant pH, the reduction of HCO-3 concentration to 50 percent and 10 percent did not alter the values of SCC and TPD, but G increased with HCO-3 reduction to 10 percent. In the absence of HCO-3, SCC, TPD and G (slightly) decreased, but 1.5 mM HCO-3 still maintained the ion transport within control values, at constant pH. Comparing PH values from 6.65 to 8.61, higher values of SCC and TPD were observed at PH 7.45, but were little affected below and above this pH. There was a significant correlation between pH and SCC and TPD values; from the regression equations (1) SCC was zero at pHs below 6.62 and above 8.78 and (2) TPD was zero below 6.50 and above 8.71