Involvement Of ATP-sensitive Potassium Channels Research Articles

The Involvement of ATP-Sensitive Potassium Channels in the Nebivolol-Induced Relaxation of Endothelium-Intact Aorta Isolated from Rats

Objective: Nebivolol is a highly selective beta-1 adrenergic receptor blocker with additional vasorelaxant properties. The vasorelaxant effect of nebivolol has been mainly attributed to endothelium-dependent mechanisms including beta-adrenergic receptors. However, the involvement of ATP-sensitive potassium (KATP) channels, another potential mechanism for vasorelaxant effect, in the vasorelaxant response to nebivolol remains unclear. Therefore, this study was aimed to investigate the role of KATP channels in the nebivolol-induced vasorelaxation in the isolated rat aorta Methods: The rat thoracic aortic rings isolated from Sprague-Dawley rats were mounted in organ bath chambers containing Krebs-Henseleit solution at 37 oC continuously bubbled with 95% O2 and 5% CO2. After an equilibration period, the presence of endothelium was confirmed by the response (more than 50%) to acetylcholine (10 μM) in aortic rings precontracted with phenylephrine (1 μM). After washout, in control group, the endothelium-intact aortic rings were contracted by potassium chloride (30 mM) before the cumulative addition of nebivolol (0.0001-100 μM). In some experiments, the relaxant response to nebivolol (0.0001-100 μM) was also obtained in the presence of glibenclamide (KATP channel blocker, 10 μM) or Nω-Nitro-L-arginine methyl ester (L-NAME: eNOS inhibitor, 100 μM) in the endothelium-intact aortic rings precontracted with potassium chloride (30 mM). Data were presented as means±SEM. Multiple comparisons of groups were performed by using ANOVA followed by post-hoc Bonferroni test. Results: Nebivolol elicited a concentration dependent vasorelaxant effect in the endothelium-intact aortic rings. Relaxant response to nebivolol was significantly inhibited by the presence of glibenclamide or L-NAME (p< 0.05). Although Emax values were not found significantly different among groups, pD2 values of nebivolol were reduced in the endothelium-intact aortic rings incubated with glibenclamide or L-NAME. Conclusion: These results demonstrate for the first time the involvement of KATP channels in the nebivolol-induced vasorelaxation in the endothelium-intact aorta precontracted with potassium chloride.

Involvement of ATP-sensitive potassium channels in effect of pinacidil on saphenous vein obtained from the patients with and without type 2 diabetes mellitus

Involvement of ATP-sensitive potassium channels in effect of pinacidil on saphenous vein obtained from the patients with and without type 2 diabetes mellitus

Possible involvement of ATP-sensitive potassium channels in the antidepressant-like effects of gabapentin in mouse forced swimming test

Gabapentin as an anticonvulsant drug also has beneficial effects in treatment of depression. Previously, we showed that acute administration of gabapentin produced an antidepressant-like effect in the mouse forced swimming test (FST) by a mechanism that involves the inhibition of nitric oxide (NO). Considering the involvement of NO in adenosine triphosphate (ATP)-sensitive potassium channels (KATP), in the present study we investigated the involvement of KATP channels in antidepressant-like effect of gabapentin. Gabapentin at different doses (5-10 mg/kg) and fluoxetine (20 mg/kg) were administrated by intraperitoneal route, 60 and 30 min, respectively, before the test. To clarify the probable involvement of KATP channels, mice were pretreated with KATP channel inhibitor or opener. Gabapentin at dose 10 mg/kg significantly decreased the immobility behavior of mice similar to fluoxetine (20 mg/kg). Co-administration of subeffective dose (1 mg/kg) of glibenclamide (inhibitor of KATP channels) with gabapentin (3 mg/kg) showed a synergistic antidepressant-like effect. Also, subeffective dose of cromakalim (opener of KATP channels, 0.1 mg/kg) inhibited the antidepressant-like effect of gabapentin (10 mg/kg). None of the treatments had any impact on the locomotor movement. Our study, for the first time, revealed that antidepressant-like effect of gabapentin in mice is mediated by blocking the KATP channels.

Involvement of ATP-sensitive potassium channels and the opioid system in the anticonvulsive effect of zolpidem in mice.

Zolpidem is a hypnotic medication that mainly exerts its function through activating γ-aminobutyric acid (GABA)A receptors. There is some evidence that zolpidem may have anticonvulsive effects. However, the mechanisms underlying this effect have not been elucidated yet. In the present study, we used the pentylentetrazole (PTZ)-induced generalized seizure model in mice to investigate whether zolpidem can affect seizure threshold. We also further evaluated the roles of ATP-sensitive potassium (KATP) channels as well as μ-opioid receptors in the effects of zolpidem on seizure threshold. Our data showed that zolpidem in a dose-dependent manner increased the PTZ-induced seizure threshold. The noneffective (i.e., did not significantly alter the PTZ-induced seizure threshold by itself) doses of KATP channel blocker (glibenclamide) and nonselective opioid receptor antagonist (naloxone) were able to inhibit the anticonvulsive effect of zolpidem. Additionally, noneffective doses of either KATP channel opener (cromakalim) or nonselective μ-opioid receptor agonist (morphine) in combination with a noneffective dose of zolpidem exerted a significant anticonvulsive effect on PTZ-induced seizures in mice. A combination of noneffective doses of naloxone and glibenclamide, which separately did not affect zolpidem effect on seizure threshold, inhibited the anticonvulsive effects of zolpidem. These results suggest a role for KATP channels and the opioid system, alone or in combination, in the anticonvulsive effects of zolpidem.

Possible involvement of ATP-sensitive potassium channels in the antidepressant-like effect of baclofen in mouse forced swimming test.

Previous study confirmed that the acute treatment with baclofen by inhibition of the l-arginine-nitric oxide (NO) pathway diminished the immobility behavior in the forced swimming test (FST) of mice. Considering the involvement of NO in adenosine triphosphate (ATP)-sensitive potassium channels (KATP), in the present study we investigated the involvement of KATP channels in antidepressant-like effect of baclofen in the forced swimming test (FST). After assessment of locomotor behavior in the open-field test (OFT), FST was applied for evaluation of the antidepressant-like activity of baclofen in mice. Baclofen at different doses (0.1, 0.3, and 1mg/kg) and fluoxetine (20mg/kg) were administrated by intraperitoneal (ip) route, 30min before the FST or OFT. To clarify the probable involvement of KATP channels, after determination of sub-effective doses of glibenclamide as a KATP channel blocker and cromakalim, as an opener of these channels, they were co-administrated with the sub-effective and effective doses of baclofen, respectively. Baclofen at dose 1mg/kg significantly decreased the immobility behavior of mice similar to fluoxetine (20mg/kg). Co-administration of gelibenclamide sub-effective dose (1mg/kg) with baclofen (0.1mg/kg) showed a synergistic antidepressant-like effect in the FST. Also, sub-effective dose of cromakalim (0.1mg/kg) inhibited the antidepressant-like effect of baclofen (1mg/kg) in the FST. All aforementioned treatments had not any impact on the locomotor movement of mice in OFT. Our study for the first time revealed that antidepressant-like effect of baclofen on mice is KATP-dependent, and baclofen seems that exert this effect by blocking the KATP channels.

Effects of exhaustive exercise on the ATP-sensitive potassium channel of rat cardiac sinoatrial node

Background: Exercise-induced cardiac arrhythmia has been of great concern in the field of sports science and sports medicine. Athletes engaged in high-intensity training are at particularly high risk of atrial fibrillation. Recent studies indicate the involvement of ATP-sensitive potassium channel (KATP channel) involved in pathophysiology changes of arrhythmias, however, the underlying mechanisms are unclear. This paper discusses the subunit mRNA and current density of KATP channel of sinoatrial node at different time phrases after exhaustive exercise.

The relaxant effect of extract of Phyllanthus urinaria in the guinea-pig isolated trachea. Evidence for involvement of ATP-sensitive potassium channels.

This study analyses the relaxation induced by the hydroalcoholic extract of stems, leaves and roots from Phyllanthus urinaria (Euphorbiaceae) in the guinea-pig trachea (GPT) pre-contracted by carbachol. The hydroalcoholic extract of P. urinaria (0.1-10 mg mL-1) caused a graded relaxation in GPT with or without epithelium, with mean EC50 values of 1.94 (1.41-2.67) and 2.00 (1.47-2.78) mg mL-1 and Emax of 717 mg (+/- 16) and 627 mg (+/- 12), respectively. The relaxation in response to hydroalcoholic extract, like that to cromakalim (EC50 3.57 (2.75-4.64 microM) in GPT without epithelium, was fully abolished in the presence of high KCl concentrations (80 mM), and was significantly attenuated by tetraethylammonium (10 or 30 mM) or glibenclamide (0.1 or 3 microM). However, the relaxation caused by the hydroalcoholic extract was unaffected by apamin (0.1 or 1.0 microM), nitro-L-arginine (L-NOARG, 100 microM), methylene blue (10 microM) or by calcitonin gene-related peptide (CGRP) (8-37) (a CGRP antagonist, 0.1 microM). Both propranolol (1 or 3 microM) and [D-p-Cl-Phe6,Leu17]VIP (a vasoactive intestinal peptide (VIP) receptor antagonist, 0.1 microM) produced a significant displacement to the right (about 2-fold) of the relaxation response to hydroalcoholic extract of P. urinaria. Thus, the present results indicate that the ATP-activated potassium channels sensitive to glibenclamide, but not the small conductance calcium-activated potassium channels sensitive to apamin, largely contribute to the relaxation effect of the hydroalcoholic extract of P. urinaria in GPT. In addition, both beta 2 and VIP-mediated responses seem to account, at least in part, for the relaxation effect of the hydroalcoholic extract, as its relaxant response was partially attenuated by both propranolol and VIP receptor antagonist.

Sildenafil attenuates TNBS‐induced colitis in rats: possible involvement of cGMP and KATP channels

The involvement of cGMP/KATP pathway in effects of sildenafil on experimental colitis was investigated. Sildenafil significantly attenuated colonic injury markers. These effects were reversed by the addition of glibenclamide or ODQ, indicating the involvement of ATP-sensitive potassium channels (KATP) and cGMP, respectively.

Diazoxide Reduces Status Epilepticus Neuron Damage in Diabetes

Diabetic hyperglycemia is associated with seizure severity and may aggravate brain damage after status epilepticus. Our earlier studies suggest the involvement of ATP-sensitive potassium channels (K(ATP)) in glucose-related neuroexcitability. We aimed to determine whether K(ATP) agonist protects against status epilepticus-induced brain damage. Adult male Sprague-Dawley rats were divided into two groups: the streptozotocin (STZ)-induced diabetes (STZ) group and the normal saline (NS) group. Both groups were treated with either diazoxide (15 mg/kg, i.v.) (STZ + DZX, NS + DZX) or vehicle (STZ + V, NS + V) before lithium-pilocarpine-induced status epilepticus. We evaluated seizure susceptibility, severity, and mortality. The rats underwent Morris water-maze tests and hippocampal histopathology analyses 24 h post-status epilepticus. A multi-electrode recording system was used to study field excitatory postsynaptic synaptic potentials (fEPSP). RNA interference (RNAi) to knockdown Kir 6.2 in a hippocampal cell line was used to evaluate the effect of diazoxide in the presence of high concentration of ATP. Seizures were less severe (P < 0.01), post-status epilepticus learning and memory were better (P < 0.05), and neuron loss in the hippocampal CA3 area was lower (P < 0.05) in the STZ + DZX than the STZ + V group. In contrast, seizure severity, post-status epilepticus learning and memory, and hippocampal CA3 neuron loss were comparable in the NS + DZX and NS + V groups. fEPSP was lower in the STZ + DZX but not in the NS + DZX group. The RNAi study confirmed that diazoxide, with its K(ATP)-opening effects, could counteract the K(ATP)-closing effect by high dose ATP. We conclude that, by opening K(ATP), diazoxide protects against status epilepticus-induced neuron damage during diabetic hyperglycemia.

Cardiovascular effects of the aqueous extract from Caesalpinia ferrea: Involvement of ATP-sensitive potassium channels

Caesalpinia ferrea is a plant very used in the folk medicine for treatment of several diseases, such as diabetes. This study investigated the cardiovascular effects of the aqueous extract from stem bark of C. ferrea (AECF). In non-anesthetized rats, AECF (10, 20, 40, 60 and 80 mg/kg; i.v.) induced hypotension (− 9 ± 1;− 12 ± 1;− 14 ± 1; − 20 ± 3 and − 51 ± 6%; respectively) and tachycardia (6 ± 1; 8 ± 1; 12 ± 2; 14 ± 2 and 26 ± 3%; respectively). Hypotension was not affected after atropine or l-NAME. Furthermore, AECF (40 mg/kg) induced atrioventricular block and extrasystoles, which was not affected after atropine. In intact rings of the rat mesenteric artery, AECF (0.001–30 mg/ml, n = 6) induced relaxations of phenylephrine tonus (Emax = 110 ± 4%), which was not changed after the removal of endothelium (Emax = 113 ± 9%). In rings without endothelium pre-contracted with KCl 80 mM, phenylephrine plus KCl 20 mM or phenylephrine plus glibenclamide, the curve to AECF was significantly attenuated (Emax = 24 ± 4%, 70 ± 5% and 62 ± 7%, respectively, n = 6), but was not affected in the presence of tetraethylammonium or 4-aminopyridine (Emax = 125 ± 15% and 114 ± 7%, respectively, n = 6). These results demonstrate that AECF induces hypotension associated to tachycardia; however, in dose of 40 mg/kg, AECF induces transient bradyarrhythmias. Furthermore, AECF induces vasodilatation in rat mesenteric artery which appears to be mediated by ATP-sensitive K + channel openings.

Beating myocardium counteracts myogenic tone of coronary microvessels: involvement of ATP-sensitive potassium channels

Myogenic tone is intrinsic to vascular tissue and plays an important role in determining basal coronary resistance. However, the effect of the beating heart on myogenic tone is unknown. We investigated the effects of myocardium-derived vasoactive factors on the myogenic tone of coronary microvessels in the resting condition and during increased metabolism. Pressurized isolated coronary vessels (detector vessel, DV) of rabbits (n = 33, maximal inner diameter 201 +/- 8 microm) were gently placed on beating hearts of anesthetized dogs and observed with an intravital microscope equipped with a floating objective. To shut off the myocardium-derived vasoactive signals, we placed plastic film between DV and the heart. The intravascular pressure was changed from 120 to 60 cmH(2)O, and pressure-diameter curves were obtained with and without the contact of DV and the myocardium. The direct contact shifted the pressure-diameter curve upward (P < 0.05 vs. without contact), and myogenic tone was reduced by approximately 40%. When endothelium of DV was denuded, the shift persisted, but the degree of shift was reduced to 10% (P < 0.05 vs. with endothelium). The shift was abolished by glibenclamide, an ATP-sensitive potassium (K(ATP)) channel blocker. A similar upward shift was induced by rapid pacing, but the shift was not blocked by glibenclamide. We conclude that the beating myocardium counteracts myogenic tone by releasing transferable vasoactive signals that affect the endothelium and the vascular smooth muscle, and that the signals are solely mediated by the activation of K(ATP) channels, unlike the rapid pacing-induced vasoactive factors.

Involvement of ATP-sensitive potassium channels in central control of gasping

Involvement of ATP-sensitive potassium channels in central control of gasping

Molecular mechanisms of cardiac protection by adaptation to chronic hypoxia.

Effective protection of the heart against ischemia/reperfusion injury is one of the most important goals of experimental and clinical research in cardiology. Besides ischemic preconditioning as a powerful temporal protective phenomenon, adaptation to chronic hypoxia also increases cardiac tolerance to all major deleterious consequences of acute oxygen deprivation such as myocardial infarction, contractile dysfunction and ventricular arrhythmias. Although many factors have been proposed to play a potential role, the detailed mechanism of this long-term protection remains poorly understood. This review summarizes current limited evidence for the involvement of ATP-sensitive potassium channels, reactive oxygen species, nitric oxide and various protein kinases in cardioprotective effects of chronic hypoxia.

O-285 - Involvement of ATP-sensitive potassium channels in the antitussive effect of moguisteine

O-285 - Involvement of ATP-sensitive potassium channels in the antitussive effect of moguisteine

A secretory mechanism of renal kallikrein by a high potassium ion; a possible involvement of ATP-sensitive potassium channel

A relatively rapid excretion of urinary kallikrein into urine was observed by an intravenous infusion of high potassium in anesthetized rats. Superfusion of sliced cortex isolated from rat kidney with an isotonic solution containing more than 20 mM of KCl significantly stimulated the release of kallikrein. The latter in vitro result supported another mechanism for the release of renal kallikrein from kidney other than biosynthesis of kallikrein by aldosterone released from adrenal cortex after loading of high potassium and the mechanism was elucidated. ATP-sensitive potassium channel blockers, glibenclamide, 4-morpholinecarboximidine-N-1-adamantyl-N′-cyclohexylhydrochloride (U37883A), and barium chloride, which inhibit an efflux of intracellular potassium to block the channel, showed a significant increase of the kallikrein release from the slice of kidney cortex. Cytochalasin B, which inhibits a polymerization of actin, also showed a stimulation of the release. Enhanced release of kallikrein by a high potassium or ATP-sensitive potassium channel blocker was reduced by the absence of calcium ion and the presence of voltage-dependent calcium channel blocker in the superfused solution. These results indicate the ATP-sensitive potassium channel which couples to voltage-dependent calcium channel and cytoskeletal protein could be involved in a rapid secretory mechanism of renal kallikrein by high potassium.

Role of KATP channel in heat shock and pharmacological preconditioning.

Heat shock (HS) and 4-monophosphoryl lipid A (MLA, a non-toxic analogue of endotoxin) protects the myocardium against ischemia-reperfusion injury. We studied the involvement of ATP-sensitive potassium channel (KATP channel) in ischemic protection induced by these stimuli. Anesthetized rabbits were preconditioned with either HS (by raising temperature to 42 degrees C for 15 min) or intravenous pretreatment with MLA (35 micrograms/kg). After 24 h, animals were re-anesthetized and subjected to 30-min regional ischemia followed by 180-min reperfusion (I/R). KATP channel blockers glibenclamide and/or 5-hydroxydecanoate (5-HD) were used to inhibit channel function. The 72 kD heat shock protein (HSP-72) was measured by Western blots. HS produced a marked reduction in infarct size (39.4 +/- 8.1% to 14.3 +/- 2.5%, p < 0.05) that was abolished by glibenclamide (42.3 +/- 3.2%) and 5-HD (33.7 +/- 4.8%) when given before I/R. These drugs failed to block HS protection when given before HS. Expression of HSP-72 was increased in all HS groups as compared to non-HS groups in both glibenclamide and 5-HD-treated rabbits. Similarly, pretreatment with MLA reduced infarct size from 40 +/- 8.6% to 15.1 +/- 1.5% (p < 0.05). The infarct size increased to 51.9 +/- 5.8 with 5-HD in MLA-treated rabbits. 5-HD did not alter infarct size significantly when given in vehicle-treated control rabbits. These data suggest that HS and MLA exert their anti-ischemic effect through activation of KATP channel.

Calcitonin gene-related peptide-induced relaxation in isolated small superior mesenteric arteries from adult stroke-prone spontaneously hypertensive rats.

1. The relaxant responses to calcitonin gene-related peptide (CGRP) of the 3rd order branches of the superior mesenteric arteries (SMA) from 6 month old stroke-prone spontaneously hypertensive rats (SHRSP) and age-matched Wistar-Kyoto (WKY) rats were studied in vitro. 2. Cumulative addition of CGRP (10(-11)-10(-7) mol/L) caused endothelium-independent relaxation of arterial rings precontracted with noradrenaline (10(-6) mol/L). A markedly increased response to CGRP was observed in SHRSP. 3. There was no significant difference between SHRSP and WKY in relaxation produced by forskolin, dibutyryl cyclic AMP and 3-isobutyl-1-methylxanthine. 4. Pretreatment with glibenclamide (10(-6) mol/L) did not affect CGRP-induced relaxation in either SHRSP or WKY. 5. These results indicated that CGRP-induced vasodilation was increased in the small branches of SMA from SHRSP, and that this increase did not seem to be associated with an augmented response to cyclic AMP or with increased involvement of ATP-sensitive potassium channels.

Choleretic action of glibenclamide in the perfused rat liver: involvement of ATP-sensitive potassium channel: [formula omitted] Dept. of Biochemistry, School of Med., Keio University, Tokyo. ∗1st Dept. of Surgery, Nagoya University, Nagoya, Japan

Choleretic action of glibenclamide in the perfused rat liver: involvement of ATP-sensitive potassium channel: [formula omitted] Dept. of Biochemistry, School of Med., Keio University, Tokyo. ∗1st Dept. of Surgery, Nagoya University, Nagoya, Japan

Glibenclamideのマクロファージにおけるコレステロールエステル合成能におよぼす影響

To clarify the process of atherosclerosis, the mechanism of cholesteryl ester accumulation in macrophages must be elucidated. Many drugs, hormones and cytokines are known to affect this process. Glibenclamide is widely used for the treatment of diabetes mellitus. However, the effects of this drug on cholesterol metabolism are not well known. In this study, we examined the effect of glibenclamide on cholesteryl ester synthesis and cellular cholesterol contents in macrophages. Glibenclamide enhanced cholesteryl ester synthesis in a concentrationdependent manner. This effect was observed both in the presence and absence of LDL. Degradation and association of 125I-LDL were not changed by glibenclamide. However, glibenclamide inhibited cholesteryl ester accumulation. These findings suggest that glibenclamide did not change the metabolism of LDL and that cholesteryl ester hydrolysis and efflux may be enhanced by glibenclamide. To study the involvement of ATP-sensitive potassium channel in the action of glibenclamide, the effect of lemakalim and nicorandil, potassium channel openers, on cholesteryl ester synthesis was examined. Neither nicorandil nor lemakalim had any effects on cellular cholesteryl ester synthesis. In addition, nicorandil did not alleviate the action of glibenclamide. These findings suggest that a factor other than the ATP-sensitive potassium channel is involved in the inhibition of cholesteryl ester accumulation by glibenclamide.

Involvement of ATP-sensitive potassium channels in preconditioning protection.

Single or multiple brief periods of ischemia (preconditioning, PC) have been shown to protect the myocardium from infarction during a subsequent more prolonged ischemic insult. To test the hypothesis that opening of ATP-sensitive potassium channels (KATP) is involved in this mechanism, either bimakalim, a KATP channel opener, or glibenclamide, a KATP channel blocker, were administered to mimic or to block preconditioning protection in barbital-anesthetized pigs. PC was elicited by a single period of 10 min left anterior descending coronary artery (LADCA) occlusion followed by 15 min of reperfusion before the LADCA was reoccluded for 60 min. Instead of PC, bimakalim infusion was started 15 min before the 60 min LADCA occlusion (TCO) and stopped with the onset of ischemia. Glibenclamide was administered either for 10 min prior to the PC protocol, before bimakalim infusion, or before TCO. Regional wall function was quantified with ultrasonic crystals aligned to measure wall thickening (% delta WT). At the end of the protocol, infarct size was determined by incubating myocardium with p-nitrobluetetrazolium. In seven preconditioned pigs, infarct size was 9.9 +/- 5.1% of the risk region compared with 65.9 +/- 6.0% in the seven control pigs subjected to 60 min of ischemia only (p < 0.001). In seven pigs treated with bimakalim, infarct size was reduced to 35.3 +/- 6.6 (p < 0.05 vs. controls). Blocking ATP-sensitive potassium channels with glibenclamide prior to PC abolished its protective effect (infarct size, 62.2 +/- 4.5%; p < 0.001 vs. PC alone). Glibenclamide also antagonized the protective effect of bimakalim (infarct size, 55.2 +/- 4.0%), but did not affect infarct size, when solely administered prior to the prolonged ischemic period (62.2 +/- 4.3%). We conclude that in swine myocardium KATP channels are involved in the protective effect of ischemic preconditioning, since glibenclamide completely abolished the protective effect of preconditioning, while bimakalim could--at least in part--mimic it.