Effect of chronic intermittent hypobaric hypoxia on relaxation of aorta and mechanisms in developing rats / 中国药理学通报

Aim To investigate the effect of chronic intermittent hypobaric hypoxia (CIHH) on relaxation of thoracic aorta rings in male developing rats and the underlying mechanisms. Methods Male neonatal Spra-gue-Dawlay ( SD) rats were randomly divided into eight groups respectively: CIHH treatment group (CIHH), group of one-week post-CIHH (CIHH-pl), group of two-week post-CIHH ( CIHH-p2 ) , group of three-week post-CIHH (CIHH-p3 ) , control group for CIHH (Con), control group for CIHH-pl (Con-1), control group for CIHH-p2 ( Con-2) and control group for CIHH-p3 (Con-3 ). Rats in CIHH groups were put into a hypobaric chamber with the mother rats 1 ~ 3 days before the birth to get a hypobaric hypoxia exposure mimicking 3 km altitude for 42 days, 5 hours daily. Rats in control groups were kept in the same environment as CIHH rats except hypoxia exposure. After anaesthetized with pentobarbital sodium (50 mg • kg-1 i. p. ), the thorax of rats was opened and thoracic aorta rings were made. The artery rings were placed in the bath chamber filled with K-H solution, and the relaxation of artery rings was recorded under normoxia or a-cute hypoxia conditions, respectively. Results (1) Under normoxia condition, the acetylcholine ( ACh)-induced relaxation of thoracic aorta increased obviously in CIHH groups compared with corresponding Con groups ( P < 0. 05 ). ( 2 ) The enhancing effect of CIHH treatment on thoracic aorta could be maintained for at least three weeks (P < 0. 05). (3 ) Under acute hypoxia condition, ACh-induced relaxation of thoracic aorta in each group decreased obviously, but the decrease in CIHH groups was significant less than that in Con groups ( P < 0.05 ). (4) The enhancement of CIHH on relaxation of thoracic aorta could be reversed by indomethacin (Indo), a cyclooxygenase inhibitor, glibenclamide (Gli), a KATP blocker, and Tempo, a free radical scavenger. Conclusions CIHH augments endothelium-dependent relaxation in thoracic aorta of developing rats. Also, CIHH can antagonize the inhibition of acute hypoxia on relaxation of thoracic aorta. The enhancing effect of CIHH treatment may be related with the increase of prostacyclin, the opening of KATP and free radical production.

A case report on congenital hyperinsulinism associated with ABCC8 nonsense mutation: Good response to octreotide / Journal of the ASEAN Federation of Endocrine Societies

@#<p style="text-align: justify;">A 2.4 kg baby boy born via Caesarian section at 35 weeks had the first onset of hypoglycemia at 2 hours of life. The infant required a glucose load of 30 mg/kg/min. Insulin level was 19.6 pmol/L (normal value 17.8-173.0) in the absence of ketosis. He was resistant to oral diazoxide but responded to octreotide infusion. The boy was found to be heterozygous for an ABCC8 nonsense mutation, p.R934*. We present our experience on the use of subcutaneous octreotide for 2 years for the treatment of diazoxide resistant congenital hyperinsulinism (CHI).</p>

Progress on neonatal diabetes mellitus / 临床儿科杂志

Most neonatal diabetes mellitus (NDM) is caused by genetic abnormality. Sulfonylurea (SU) has been successfully applied in NDM patients;The pathogenesis of NDM and mechanism of sulfonylurea on molecular level have been illuminated, and recent studies revealed that glycated albumin is a useful glycemic indicator. In this review, the research progress of NDM is summarized.

Scanning and analysis of the KATP channel mutations in 12 cases of infancy onset type 1 diabetes mellitus / 中华实用儿科临床杂志

Objective To screen the mutation of KATP channel mutations in Chinese pedigrees with infantile onset type 1 diabetes mellitus (T1DM) and neonatal diabetes mellitus.Methods A cohort of 12 children of infant onset T1DM and neonatal diabetes mellitus admitted into Beijing Children's Hospital between March 2004 and June 2013 were selected.PCR amplification and direct sequencing were used to analyze the 39 exons of ABCC8 gene and one exon of KCNJ11.And the mutational sites of the parents of the probands was sequenced in order to identify the inheritance.Results Analysis revealed ABCC8 mutation in 25％ (3/12 cases) of the patients,a case of transient neonatal diabetes (TNDM),a case of permanent neonatal diabetes mellitus (PNDM) and a case of infant onset T1DM.All positive patients showed a known heterozygosis mutation in the ABCC8 gene(R1182Q,c.3545G ＞ A,D209E,c.627C ＞ G,E208K c.622G ＞ A).The residue R1182Q,which was located at a position involved in joining transmembrane domain 2 to nucleotide binding domain 2,the mutations E208K and D209E were located in the intracellular region that links the transmembrane domain with the gatekeeper module.All the three mutations were located throughout the cytoplasm part of SUR1 protein.The TNDM successfully transferred from insulin to oral sulfonylureas therapy.Conclusions There is a complex genetic pathogenesis in neonatal and infant-onset diabetes.The KATP channel activating mutations is one of the main causes of neonatal diabetes mellitus and may cause T1DM in infants in China.Oral Glibenclamide therapy seems highly effective for some patients with the KATP channel activating mutations.

Effect of estrogens on ATP-sensitive potassium channel activity in isolated mouse ventricular cardiomyocytes / 中国比较医学杂志

Objective To study the effects of estrogens ( 17α-ethynylestradiol and 17β-estradiol ) on the ATP-sensitive potassium channel ( KATP ) activities in the enzymatically ( collagenase and protease ) isolated ICR mouse ventricular cardiomyocytes using inside-out and cell-attached patch clamp techniques .Methods In the inside-out patch configurations, the two estrogens reduced the K ATP channel activities in a dose-dependent manner at -60 mV holding potential ( HP) .Results The half-maximal inhibitory concentration ( IC50 ) of the 17α-esthynylestradiol and the 17β-estradiol were 0.3μmol/L and 0.1 nmol/L, respectively.However, these agents had no effects on the pinacidil-and DNP-induced KATP channel activities in the cell-attached patch configuration.However, the inhibitory effect of KATP channel activities by the 17-estrogens or the anti-estrogens in the excised inside-out patch configuration were abolished by 1 pmol/L PDBu.Conclusions The results of this study demonstrate that some estrogens decrease the K ATP channel activity acting on the inside of the isolated cardiomyocytes , and play a protective role to cardiomyocytes .

An ABCC8 gene mutation leading to the onset of KATP-congenital hyperinsulinism in a Chinese boy and his pedigree analysis / 中华内分泌代谢杂志

ABCC8,KCNJ11,and GLUD1 gene mutations were investigated in a male patient with congenital hyperinsulinism and his parents were also investigated.A 1484 G＞A mutation was found in the 10th exon of ABCC8 gene in the patient,which leads to amino acid substitution at the 495 residue of the sulphonylurea receptor SUR1 protein.The patient's father also carried the same heterozygous inactive mutation,while the genotype of the mother was normal,indicating that the gene mutation of the patient was paternally inherited.According to that mutation,it is deduced that the patient may suffer from the focal type of congenital hyperinsulinism.

Participation of KATP Channels in the Antinociceptive Effect of Pregabalin in Rat Formalin Test

BACKGROUND: Pregabalin is an anticonvulsant and analgesic agent that interacts selectively with the voltage-sensitive-Ca(2+)-channel alpha-2-delta subunit. The aim of this study was to evaluate whether the analgesic action of intrathecal (IT) pregabalin is associated with KATP channels in the rat formalin test. METHODS: IT PE-10 catheters were implanted in male Sprague-Dawley rats (250-300 g) under inhalation anesthesia using enflurane. Nociceptive behavior was defined as the number of hind paw flinches during 60 min after formalin injection. Ten min before formalin injection, IT drug treatments were divided into 3 groups: normal saline (NS) 20 microl (CON group); pregabalin 0.3, 1, 3 and 10 microg in NS 10 microl (PGB group); glibenclamide 100 microg in DMSO 5 microl with pregabalin 0.3, 1, 3 and 10 microg in NS 5 microl (GBC group). All the drugs were flushed with NS 10 microl. Immunohistochemistry for the KATP channel was done with a different set of rats divided into naive, NS and PGB groups. RESULTS: IT pregabalin dose-dependently decreased the flinching number only in phase 2 of formalin test. The log dose response curve of the GBC group shifted to the right with respect to that of the PGB group. Immunohistochemistry for the KATP channel expression on the spinal cord dorsal horn showed no difference among the groups 1 hr after the formalin test. CONCLUSIONS: The antinociceptive effect of pregabalin in the rat formalin test was associated with the activation of the KATP channel. However, pregabalin did not induce KATP channel expression in the spinal cord dorsal horn.

Ameliorating Effects of Sulfonylurea Drugs on Insulin Resistance in Otsuka Long-Evans Tokushima Fatty Rats

OLETF (Otsuka Long-Evans Tokushima Fatty) rats are characterized by obesity-related insulin resistance, which is a phenotype of type 2 diabetes. Sulfonylurea drugs or benzoic acid derivatives as inhibitors of the ATP-sensitive potassium (KATP) channel are commercially available to treat diabetes. The present study compared sulfonylurea drugs (glimepiride and gliclazide) with one of benzoic acid derivatives (repaglinide) in regard to their long-term effect on ameliorating insulin sensitivity in OLETF rats. Each drug was dissolved and fed with drinking water from 29 weeks of age. On high glucose loading at 45 weeks of age, response of blood glucose recovery was the greatest in the group treated with glimepiride. On immunohistochemistry analysis for the Kir6.2 subunit of KATP channels, insulin receptor beta-subunits, and glucose transporters (GLUT) type 2 and 4 in liver, fat and skeletal muscle tissues, the sulfonylurea drugs (glimepiride and gliclazide) were more effective than repaglinide in recovery from their decreased expressions in OLETF rats. From these results, it seems to be plausible that KATP-channel inhibitors containing sulfonylurea moiety may be much more effective in reducing insulin resistance than those with benzoic acid moiety. In contrast to gliclazide, non-tissue selectivity of glimepiride on KATP channel inhibition may further strengthen an amelioration of insulin sensitivity unless considering other side effects.

Protein Kinase C Activates ATP-sensitive Potassium Channels in Rabbit Ventricular Myocytes

Several signal transduction pathways have been implicated in ischemic preconditioning induced by the activation of ATP-sensitive K+ (KATP) channels. We examined whether protein kinase C (PKC) modulated the activity of KATP channels by recording KATP channel currents in rabbit ventricular myocytes using patch-clamp technique and found that phorbol 12, 13-didecanoate (PDD) enhanced pinacidil-induced KATP channel activity in the cell-attached configuration; and this effect was prevented by bisindolylmaleimide (BIM). KATP channel activity was not increased by 4alpha-PDD. In excised inside-out patches, PKC stimulated KATP channels in the presence of 1 mM ATP, and this effect was abolished in the presence of BIM. Heat-inactivated PKC had no effect on channel activity. PKC-induced activation of KATP channels was reversed by PP2A, and this effect was not detected in the presence of okadaic acid. These results suggest that PKC activates KATP channels in rabbit ventricular myocytes.

Thiol-dependent Redox Mechanisms in the Modification of ATP-Sensitive Potassium Channels in Rabbit Ventricular Myocytes

Cellular redox state is known to be perturbed during ischemia and that Ca2+ and K+ channels have been shown to have functional thiol groups. In this study, the properties of thiol redox modulation of the ATP-sensitive K+ (KATP) channel were examined in rabbit ventricular myocytes. Rabbit ventricular myocytes were isolated using a Langendorff column for coronary perfusion and collagenase. Single-channel currents were measured in excised membrane patch configuration of patch-clamp technique. The thiol oxidizing agent 5, 5'-dithio-bis- (2-nitro-benzoic acid) (DTNB) inhibited the channel activity, and the inhibitory effect of DTNB was reversed by dithiothreitol (disulfide reducing agent; DTT). DTT itself did not have any effect on the channel activity. However, in the patches excised from the metabolically compromised cells, DTT increased the channel activity. DTT had no effect on the inhibitory action by ATP, showing that thiol oxidation was not involved in the blocking mechanism of ATP. There were no statistical difference in the single channel conductance for the oxidized and reduced states of the channel. Analysis of the open and closed time distributions showed that DTNB had no effect on open and closed time distributions shorter than 4 ms. On the other hand, DTNB decreased the life time of bursts and increased the interburst interval. N-ethylmaleimide (NEM), a substance that reacts with thiol groups of cystein residues in proteins, induced irreversible closure of the channel. The thiol oxidizing agents (DTNB, NEM) inhibited of the KATP channel only, when added to the cytoplasmic side. The results suggested that metabolism-induced changes in the thiol redox can also modulate KATP channel activity and that a modulatory site of thiol redox may be located on the cytoplasmic side of the KATP channel in rabbit ventricular myocytes.

Differential Changes of ATP-sensitive Potassium Channel Current after Hypoxia-reperfusion Treatment in Mouse Neuroblastoma 2a (N2a) Cell

Ischemic damage is one of the most serious problems. The openers of KATP channel have been suggested to have an effect to limit the ischemic damage. However, it is not yet clear how KATP channels of a cell correspond to hypoxic damage. To address the question, N2a cells were exposed to two different hypoxic conditions as follows: 6 hours hypoxia followed by 3 hours reperfusion and 12 hours hypoxia followed by 3 hours reperfusion. As the results, 6 hours hypoxic treatment increased glibenclamide-sensitive basal KATP current activity (approximately 6.5-fold at 0 mV test potential) when compared with nomoxic condition. In contrast, 12 hours hypoxic treatment induced a relatively smaller change in the KATP current density (2.5-fold at 0 mV test potential). Additionally, in experiments where KATP channels were opened using diazoxide, the hypoxia for 6 hours significantly increased the current density in comparison to control condition (p < 0.001). Interestingly, the augmentation in the KATP current density reduced after exposure to the 12 hours hypoxic condition (p < 0.001). Taken together, these results suggest that KATP channels appear to be recruited more in cells exposed to the 6 hours hypoxic condition and they may play a protective role against hypoxia-reperfusion damage within the time range.

The Effect of Trifluoroacetic Acid, a Metabolite of Isoflurane on the ATP-sensitive Potassium Channel in Rabbit Ventricular Myocytes / 대한마취과학회지

BACKGROUND: Activation of ATP-sensitive K+ channels (KATP channels) in the cardiac muscle produces cardioprotective effects during myocardial ischemia. Previous experimental evidence indicates that volatile anesthetics exert beneficial actions in ischemic myocardium and enhance functional recovery of stunned myocardium. More recently, volatile anesthetics have been demonstrated to produce cardioprotective effects in stunned myocardium in vivo, and these effects are blocked by a KATP channel antagonist. This finding suggests that KATP channel activation by isoflurane may mediate antiischemic effects. However, it was demonstrated that isoflurane inhibited KATP channel activity in rabbit ventricular myocytes. To explain the discrepancy, the present investigation tested the hypothesis that isoflurane and its metabolite, trifluoroacetic acid, contributes to the activation of KATP channels in rabbit ventricular myocytes. METHODS: Single ventricular myocytes were isolated from rabbit hearts by an enzymatic dissociation procedure. Single-channel currents were measured in inside-out patch configurations of the patch-clamp technique. The perfusing liquid was equilibrated with isoflurane by passing 100% O2 through a vaporizer. RESULTS: Isoflurane inhibited KATP channel activity without a change in the single-channel conductivity. Isoflurane decreased the burst duration and increased the interburst duration. In addition, isoflurane diminished the ATP sensitivity of KATP channels. Trifluoroacetic acid, a metabolite of isoflurane, enhanced the channel activity in a dose-dependent fashion. Trifluoroacetic acid increased the burst duration and decreased the interburst duration without a change in the single-channel conductivity. Isoflurane and trifluoroacetic acid diminished the ATP sensitivity of KATP channels. CONCLUSIONS: These results imply that isoflurane and its metabolite could mediate cardioprotective effects via KATP channel activation during myocardial ischemia.

Physiological Roles and Properties of Ion Channels in Corporal Smooth Muscle / 대한남성과학회지

Decreased penile vascular resistance induced by corporal smooth muscle relaxation is the most important step in penile erection. The heightened tone of the corporal smooth muscles is considered a major cause in impotence. Modulation of corporal smooth muscle tone is a complex process requiring the integration of a host of intracellular events and extracellular signals. In intracellular events of corporal smooth muscle cell, the potassium channels and calcium channels play a major role. Functionally, potassium channels are important regulators of smooth muscle membrane potential in response to depolarizing stimuli and they counteract calcium channels. Potassium channels have been shown to play a fundamental role in both the physiologic and pathophysiologic regulation of smooth muscle tone in diverse tissues. Among the several subtypes of potassium channels, the calcium-sensitive potassium channel subtypes (KCa channel) and ATP-dependent potassium channel subtypes (KATP channel) are thought to be the most physiologically relevant in human corporal smooth muscle. With respect to intercellular communication, gap junction channels (connexin 43) are important in corporal smooth muscle cells. Thanks to gap junction channels, the signal of one cell can be spread to adjacent cells and coordination of corporal tissue response is possible. This report reviews the known details concerning junctional and nonjunctional ion channels in corporal smooth muscle and suggest the possibility of gene therapy targeting ion channels for erectile dysfunction

Protective Roles of Adenosine A1 Receptor Agonist and KATP Channel Opener in Adriamycin induced Cardiac Toxicity / 체질인류학회지

Although adriamycin is a potent chemotherapeutic agent, it elicits serious adverse effects, including cardiac toxicity. Evidence suggests that congestive heart failure induced by adriamycin is mediated by oxidative stress. We investigated whether regulators of adenosine A1 receptor and KATP channel, which have been demonstrated to mediate protective effects of ischemic -preconditioning in myocardium, are able to modulate adriamicin -induced impairment of cardiomyocyte. To study the effect of antioxidant, adenosine A1 receptor agonist & antagonist and KATP channel agonist & antagonist, ICR mice were pretreated with Cu,Zn -SOD, dimethyl thiourea, RPIA (R (-)N6 -(2 -Phenylisopropropyl)- adenosine, adenosine A1 receptor agonist), 8 -CPDPX (8 -Cyclopentyl -1, 3 -dipropylxanthine, adenosine A1 receptor antagonist), Pinacidil (KATP channel opener) and glibenclamide (KATP channel closer), followed by i.p injection with adriamycin. Mice were sacrificed day 1 or day 4 after adriamycin injection and cardiac toxicity was accessed by measurement of creatine phosphokinase (CK) levels in serum, immunohistochemistry using anti -Bcl -2 antibody and TUNEL histochemical assay. As expected, pretreatment of mice with Cu, Zn -SOD and DMTU reduced the frequency of TUNEL positive cells, indicating antioxidants protected cardiocytes from adriamycin -induced apoptosis. Interestingly, pretreatment with RPIA and pinacidil induced a significant decrease in adriamycin -induced cytotoxicity, whereas 8 -CPDPX and glibenclamide generated the opposite results. In Bcl -2 immunohistochemistry, an increased expression of Bcl -2 was found in all ADR treated groups, especially in glibenclamide pretreated group, and 8 -CPDPX pretreated groups, but Bcl -2 failed to protect myocytes from apoptosis. All ADR treated groups exhibited elevated levels of serum CK, compared with nomal controls, especially mice sacrificed at day 4 than those at day 1, and showed similar patterns of TUNNEL assay, reflecting heart tissue damages. This observation implicated cytoprotective roles of RPIA and pinacidil against adriamycin -induced cardiac toxicity. In conclusion, these results demonstrated that adriamycin -induced cardiotoxicity was associated with the generation of reactive oxygen species and that regulators including SOD, DMTU, RPIA and pinacidil elicited protective effects on this toxicity. In particular, pinacidil, the KATP channel opener, was more effective than RPIA, the adenosine A, receptor agonist, to attenate the adriamycin -induced cardiac toxicity.

Opening of ATP-sensitive K+ channel by pinacidil requires serine/threonine phosphorylation in rat ventricular myocytes

The influences of specific protein phosphatase and protein kinase inhibitors on the ATP-sensitive K+ (KATP) channel-opening effect of pinacidil were investigated in single rat ventricular myocytes using patch clamp technique. In cell-attached patches, pinacidil (100 muM) induced the opening of the KATP channel, which was blocked by the pretreatment with H-7 (100 muM) whereas enhanced by the pretreatment with genistein (30 muM) or tyrphostin A23 (10 muM). In inside-out patches, pinacidil (10 muM) activated the KATP channels in the presence of ATP (0.3 mM) or AMP-PNP (0.3 mM) and in a partial rundown state. The effect of pinacidil (10 muM) was not affected by the pretreatment with protein tyrosine phosphatase 1B (PTP1B, 10 mug ml-1), but blocked by the pretreatment of protein phosphatase 2A (PP2A, 1 U ml-1). In addition, pinacidil (10 muM) could not induce the opening of the reactivated KATP channels in the presence of H-7 (100 muM) but enhanced it in the presence of ATP(1 mM) and genistein (30 muM). These results indicate that the KATP channel-opening effect of pinacidil is not mediated via phosphorylation of KATP channel protein or associated protein, although it still requires the phosphorylation of serine/threonine residues as a prerequisite condition.

Effect of prostaglandins D2, E2 and I2 on the regulation of KATP channel activity in rat cardiac myocytes

Contribution of prostaglandins D2, E2 and I2 (PGD2, PGE2 and PGI2) on the regulation of ATP-sensitive K+ channel (KATP channel) was investigated in isolated single rat ventricular cardiac myocytes using the patch clamp technique. PGD2, PGE2 and PGI2 did not affect KATP channel activity in the inside-out patch, but increased channel activity in a dose-dependent manner when the channel activities were attenuated by the administration of 100 muM ATP to the internal solution in the inside-out patch. Channel activations by the prostaglandins were abolished by 50 muM glibenclamide, a KATP channel blocker. Dose-response curves of relative channel activity against the ATP concentrations of internal solution in the inside-out patch were shifted to the right in the presence of those three prostaglandins. The rank order of the channel stimulatory potencies (as IC50 for ATP) calculated from the dose-response curves were PGI2 < PGD2 < PGE2. Conductance of the channel was not changed by those three prostaglandins. In conclusion, we suggest that prostaglandins D2, E2 and I2 are involved in the regulation of KATP channel activity in certain circumstances, and that those three prostaglandins may cause myocardial relaxation by opening KATP channels, thus protecting the heart from ischema.

The myocardial protective role of KATP channel activation and shortening of monophasic action potential duration by ischemic preconditioning in cat / 대한내과학회지

BACKGROUND: This study was designed to evaluate the role of KATP channel activation and change of monophasic action potential duration on cardioprotective effect of ischemic preconditioning in cat. METHODS: 34 cats were divided into 4 groups: control (n=10), ischemic preconditioning(n=8), glibenclamide pre-treated(n=8) and nicorandil pre-treated group(n=8). Ischemic preconditioning was done in ischemic preconditioning and glibenclamide pre-treated groups by 3 episodes of 5 min ischemia and 10 min reperfusion. All subjects underwent 40 min of ischemia and 40 min reperfusion. The KATP channel antagonist glibenclamide was given as intravenous bolus (0.5mg/kg) 10 min before ischemic precondtioning and infused (5 microgram/min) during ischemic preconditioning. Nicorandil, a KATP channel opener was injected as intravenous bolus (0.5mg/kg) before 40 min ischemic procedure. Monophasic action potential duration at 50% repolarization(MAP50) was measured in the ischemic and non-ischemic area respectively by epicardial probe throughout the experiment. The effects of ischemic preconditioning were determined by infarct size (% area at risk). RESULTS: Ischemic preconditioning or pretreatment with nicorandil prior to 40 min ischemia demonstrated a significant reduction in infarct size(26.6+/-7%, 33+/-8% infarction of the risk zone, respectively, p<0.01, p<0.05 vs. control) with respect to control(42+/-7% infarction of the risk zone). Pretreatment with glibenclamide abolished the effect of ischemic preconditioning(40+/-8% infarction of the risk zone, p=NS vs. control) Ischemic preconditioning group exhibited a significant reduction of ischemic area MAP50 duration in the ischemic area during preconditioning; at first preconditioning 123+/-9msec vs. 137+/-19msec control(p=NS), at second preconditioning 105+/-16msec vs. 140+/-19msec control(p<0.01), at third preconditioning 109+/-15msec vs. 138+/-19msec control(p<0.05). Pretreatment with glibenclamide prevented the reduction of MAP50 in the ischemic area during ischemic preconditioning. During 40 minutes ischemia, MAP50 shortening was more pronounced in the preconditioned group than in control group; at 10 min 85+/-22 msec vs. 131+/-31msec control(p<0.05), at 20 min 88+/-21msec vs. 130+/-32msec control(p<0.05), and at 30 min 103+/-24msec vs. 136+/-30msec control(p<0.05). This shortening effect was prevented by glibenclamide pretreatment. Nicorandil pretreatment pronounced the ischemic shortening of MAP50 in ischemic area and the nicorandil effect was most significant during early ischemic period; at 10 min 97+/-21msec(p<0.05 vs. control), at 20 min 104+/-32msec (p=NS vs. control), and at 30 min 134+/-28msec(p=NS vs. control). MAP50 measured in non-ischemic area was not significantly different between groups. CONCLUSION: We conclude that KATP channel activation and monophasic action potential duration shortening play a important role in myocardial protection during ischemic injury.

The Myocardial Protective Effect and Change of the Monophasic Action Potential Duration by Adenosine Receptor, Protein Kinase C and KATP Channel in Ischemic Preconditioning in Cats

BACKGROUND AND OBJECTIVES: The myocardial protective effect of ischemic preconditioning is well known. However, the mechanism is remains unclear. The purpose of this study is to determine the role of adenosine, protein kinase C, KATP channel and the change of monophasic action potential duration on cardioprotective effect of ischemic preconditioning in cat. Materials AND METHODS: In this experiment, 66 cats were allocated into 7 groups:control (n=10), ischemic preconditioning (n=10), adenosine pre-treated (n=10), SPT (8-p-sulfophenyl theophylline) pre-treated (n=9), polymyxin B pre-treated (n=9), glibenclamide pre-treated (n=9) and nicorandil pre-treated (n=9) groups. Ischemic preconditioning was performed in ischemic preconditioning, SPT pre-treated, polymyxin B pre-treated and glibenclamide pre-treated groups by 3 episodes of 5 minutes ischemia and 10 minutes reperfusion. All animals were subjected to 40 minutes of ischemia and 40 minutes reperfusion. Monophasic action potential duration at 50% repolarization (MAP50) was measured in the ischemic and non-ischemic area respectively by epicardial probe throughout the experiment. The effect of ischemic preconditioning was determined by infarct size (% area at risk). RESULTS: Ischemic preconditioning, adenosine pre-treatment and nicorandil pre-treatment groups demonstrated a significant reduction in infarct size (26+/-4%, 25+/-4% and 34+/-8% infarction of the risk zone, respectively, p<0.01, p<0.01 and p<0.05 vs. control) with respect to control (41+/-8% infarction of the risk zone). However, pretreatment with SPT, polymyxin B or glibenclamide abolished the effect of ischemic preconditioning. Ischemic preconditioning group exhibited a significant reduction of MAP50 duration in the ischemic area during preconditioning;at the first preconditioning 128+/-11 msec vs. 144+/-10 msec control, at the second preconditioning 110+/-10 msec vs.147+/-10 msec control (p<0.01), at the third preconditioning 114+/-10 msec vs. 145+/-11 msec control (p<0.05). But, pretreatment with SPT, polymyxin B and glibenclamide prevented the reduction of MAP50 in the ischemic area during ischemic preconditioning. During 40 minutes ischemia, the shortening of MAP50 was more pronounced in the preconditioned group than in control group;at 5 minutes 112+/-13 msec vs. 124+/-10 msec control, at 10 minutes 89+/-12 msec vs. 133+/-11 msec control (p<0.05 ), at 20 minutes 93+/-12 msec vs. 136+/-11 msec control (p<0.05), and at 30 minutes 107+/-19 msec vs. 144+/-14 msec control (p<0.05). In adenosine pre-treated group, the MAP50 was significantly shortened than control group throughout 40 minutes occlusion period;at 5 minutes 90+/-8 msec (p<0.05), at 10 minutes 77+/-9 msec (p<0.05), at 20 minutes 92+/-8 msec (p<0.05), and at 30 minutes 103+/-8 msec (p<0.05). Nicorandil pretreatment pronounced the ischemic shortening of MAP50 in ischemic area and the effect was significant during early ischemic period;at 10 minutes 98+/-22 msec (p<0.05 vs. control). In pretreatment groups with SPT, polymyxin B or glibenclamide, the ischemic preconditioning of MAP50 measured in non-ischemic area was not significantly different compared with control group. MAP50 measured in ischemic area during reperfusion was not significantly different between groups. CONCLUSION: Based on this study, adenosine receptor-protein kinase C-KATP channel activation and monophasic action potential duration shortening during ischemia play an important role in myocardial protection during ischemic injury.

Comparative Studies of KATP Channel Openers in Penile Erection: Minoxidil, Diazoxide and Pinacidil / 대한비뇨기과학회지

PURPOSE: Currently available K+-channel openers are exclusively KATP channel openers. Among the KATP channel openers, minoxidil and diazoxide have been already used as antihypertensive agents clinically but their erectogenic activities have not been demonstrated. We performed this study to identify the effects of intracavernosal minoxidil and diazoxide on feline penile erection and also to compare that of pinacidil, relatively well-demonstrated K+-channel opener. MATERIALS AND METHODS: Using a feline model, the magnitude of penile erection caused by pinacidil was compared with that caused by minoxidil and diazoxide. With control erectile responses of intracavernosal PGE1 and papaverine, synergistic effects of erectogenic agents with KATP channel openers were also investigated in twenty-eight male cats in vivo. RESULTS: Intracavernosal injection of pinacidil increased intracavernosal pressure (ICP) in a dose-dependent fashion but minoxidil and diazoxide did not affect ICP significantly. Furthermore, pinacidil (10-5M/ml) enhanced the increase of ICP by PGE1 or papaverine but minoxidil and diazoxide did not. Noteworthy, pinacidil induced cavernous relaxation to the following erectogenic agents even in refractory cases to higher concentration (10-1M/ml) of erectogenic agent alone (n=7, p<0.01). CONCLUSIONS: These result suggests that minoxidil and diazoxide, which have been used as antihypertensive agents clinically, do not affect intracavernosal pressure. Among the KATP channel openers, pinacidil seems to be promising in producing penile erection as an alternate component of previous intracavernous injection. Also, pinacidil may be useful clinically because of the potential therapeutic effects as an intracavernosal agents in combination with PGE1 or papaverine.

Effect of Intracellular ATP on Zn2+ Blockade of KATP Channels in Pancreatic Beta Cells

In the therapeutic or the nutritional aspects, Zn2+ has been used as a supplement in a variety of drugs. Most of divalent or trivalent cations affect ion channels in the cell membranes of various organs. In particular, Zn2+ has been regarded as a potassium (K+) channel blocker in the field of electrophysiology. ATP-sensitive K+ (KATP) channel, which is a kind of inward rectifier K+ channel, resides in the cell membrane of pancreatic beta cells and plays an important role in glucose-induced insulin secretion. The glucose increases intracellular ATP concentration, and this inhibits KATP channels. The inhibition of KATP channels activity depolarizes the cell, and subsequently, insulin is released by Ca2+ influx through the voltage- gated Ca2+ channels. Here, we demonstrate that KATP channels in the pancreatic beta cells are also the targets of extracellular Zn2+ blockade and its blockade is dependent on intracellular ATP concentration. This may be a compensatory mechanism preventing the oversecretion of insulin from the Pancreatic beta cells triggered by Zn2+ intake in a physiologically fasting condition.