ATP Channel Blocker Research Articles

Iptakalim protects PC12 cell against H 2O 2-induced oxidative injury via opening mitochondrial ATP-sensitive potassium channel

The final common pathway in the demise of dopaminergic neurons in Parkinson’s disease may involve oxidative stress and excitotoxicity. In this study, we examined the neuroprotective effects of a novel ATP-sensitive potassium channel (K ATP) opener, iptakalim (IPT), against H 2O 2-induced cytotoxicity in rat dopaminergic PC12 cells. Pretreatment with IPT could attenuate increased extracellular glutamate levels and inhibit calcium influxing induced by H 2O 2. Moreover, IPT regulated the expressions of bcl-2 and bax which were responsible for inhibiting apoptosis in PC12 cells. These protective effects of IPT were abolished by selective mitoK ATP channel blocker 5-hydroxydecanoate. Therefore, IPT can protect PC12 cells against H 2O 2-induced oxidative injury via activating mitoK ATP channel.

Influence of ATP-dependent K + channels on nicotine-induced inhibition of withdrawal in morphine-dependent mice

In the present study, we have investigated the effect of nicotine and diazoxide, a potassium channel opener and glibenclamide, a potassium channel (K ATP) blocker on naloxone-precipitated physical withdrawal signs, including jumping and diarrhea. Then, the interactions of nicotine with diazoxide and glibenclamide were tested. Mice were rendered dependent on morphine by subcutaneous (s.c.) injections of morphine sulphate 3 times a day for 3 days, and jumping behavior and diarrhea were induced by intraperitoneal (i.p.) administration of naloxone 2 h after the 10th injection of morphine sulphate on day 4. Nicotine was administered 15 min and diazoxide and glibenclamide 30 min before naloxone injection. Nicotine (0.01–1 mg/kg, s.c.) and (0.1–1 mg/kg) reduced withdrawal jumping and diarrhea respectively. Diazoxide (8–64 mg/kg, i.p.) decreased jumping behavior significantly, but had no significant effect on diarrhea. On the other hand glibenclamide (0.25–1 mg/kg i.p.) and (1 mg/kg) augmented jumping and diarrhea respectively. The response of nicotine on jumping or on diarrhea was potentiated by diazoxide and decreased by glibenclamide pretreatment. The isobolographic analysis revealed synergistic interaction between diazoxide and nicotine on decreasing physical withdrawal signs including jumping and diarrhea in morphine-dependent mice. According to these results the interaction of nicotine with the K ATP channel opener and blocker in morphine physical withdrawal signs could be explained by direct and indirect effects of nicotine on membrane potassium currents.

Glibenclamide attenuates the antiarrhythmic effect of endotoxin with a mechanism not involving K ATP channels

The role of K ATP channels in the antiarrhythmic effect of Escherichia coli endotoxin-induced nitric oxide synthase (iNOS) was examined in an anesthetised rat model of myocardial ischemia and reperfusion arrhythmia by using glibenclamide (1 mg kg − 1 ), nateglinide (10 mg kg − 1 ) and repaglinide (0.5 mg kg − 1 ). Endotoxin (1 mg kg − 1 ) was administered intraperitoneally 4 h before the occlusion of the left coronary artery and glibenclamide, nateglinide or repaglinide was administered 30 min before coronary artery occlusion. We also evaluated the effects of K ATP channel blockers and nonselective K + channel blocker tetraethylammonium (TEA) on cardiac action potential configuration in the atria obtained from endotoxemic rats. The mean arterial blood pressure of rats receiving endotoxin was lower during both the occlusion and reperfusion periods. Endotoxin significantly reduced the total number of ectopic beats and the duration of ventricular tachycardia. Glibenclamide, but not nateglinide and repaglinide, prevented the hypotension and antiarrhythmic effects of endotoxin. Atria obtained from endotoxin-treated rats had prolonged action potential duration. This effect was abolished with pretreatment of iNOS inhibitors, l-canavanine and dexamethasone and perfusion of glibenclamide, but not with TEA and non-sulfonylurea drug, nateglinide. We demonstrated that glibenclamide inhibits the antiarrhythmic effect of endotoxin and this effect does not appear to involve K ATP channels.

Oleanolic acid, a pentacyclic triterpene attenuates capsaicin-induced nociception in mice: Possible mechanisms

The anti-inflammatory pentacyclic triterpene, oleanolic acid (OA) was examined on acute nociception induced by intraplantar injection of capsaicin in mice. OA administered orally to mice at 10, 30 and 100 mg kg −1, significantly attenuated the paw-licking response to capsaicin (1.6 μg/paw) by 53%, 68.5% and 36.6%, respectively. Ruthenium red (3 mg kg −1, s.c.), a non-competitive vanilloid receptor (V1, TRPV1)-antagonist also suppressed the capsaicin nociception by 38.6%. The maximal antinociception produced by 30 mg kg −1 OA was significantly blocked in animals pre-treated with naloxone (2 mg kg −1, i.p.), the opioid antagonist; l-arginine (600 mg kg −1, i.p.), the substrate for nitric oxide synthase; or glibenclamide (2 mg kg −1, i.p.), the K ATP-channel blocker, but was unaffected by yohimbine (2 mg kg −1, i.p.), an α 2-adrenoceptor antagonist. In open-field and rota-rod tests that detect motor deficits, mice received 30 mg kg −1 OA did not manifest any effect per se, indicating that the observed antinociception is not a consequence of motor abnormality. These data suggest that OA inhibits capsaicin-evoked acute nociception due to mechanisms possibly involving endogenous opioids, nitric oxide, and K ATP-channel opening.

Nicorandil reduces myocardial no-reflow by protection of endothelial function via the activation of K ATP channel

Introduction It has been found that nicorandil can attenuate myocardial no-reflow. However, the exact cause of this beneficial effect has remained unclear. We investigated whether the beneficial effect of nicorandil on myocardial no-reflow could be partly due to its protection against endothelial dysfunction. Methods Ligation area and area of no-reflow were determined echocardiographically and pathologically in sixty-two animals randomized into 7 study groups: 9 controls, 9 nicorandil-treated, 8 glibenclamide (K ATP channel blocker)-treated, 10 N G-monomethyl- l-arginine ( l-NMMA, nonselective nitric oxide synthase antagonist)-treated, 10 nicorandil and glibenclamide-treated, 8 nicorandil and l-NMMA-treated and 8 sham-operated. The acute myocardial infarction and reperfusion model was created with one 3-h occlusion of the left anterior descending coronary artery followed by 2 h of reperfusion. Constitutive nitric oxide synthase (cNOS) activity and inducible nitric oxide synthase (iNOS) activity were also quantified. Results Compared with the control group, nicorandil significantly improved ventricular function, increased coronary blood flow volume ( P < 0.01), decreased area of no-reflow and reduced necrosis area. Nicorandil also increased the cNOS activity and decreased iNOS activity ( P < 0.05). l-NMMA and glibenclamide abrogated the effects of nicorandil on ventricular function, coronary blood flow volume, area of no-reflow, necrosis area and cNOS activity, but not iNOS activity. Conclusions The beneficial effect of nicorandil on myocardial no-reflow could be due to its protection of endothelial function via the activation of K ATP channel.

Upstream signaling of protein kinase C-ε in xenon-induced pharmacological preconditioning: Implication of mitochondrial adenosine triphosphate dependent potassium channels and phosphatidylinositol-dependent kinase-1

Xenon elicits preconditioning of the myocardium via protein kinase C-ε. We determined the implication of (1) the mitochondrial adenosinetriphosphate dependent potassium (K ATP) channels and (2) the 3′phosphatidylinositol-dependent kinase-1 (PDK-1) in activating protein kinase C-ε. For infarct size measurements, anaesthetized rats were subjected to 25 min of coronary artery occlusion followed by 120 min of reperfusion. Rats received xenon 70% during three 5-min periods before ischaemia with or without the K ATP channel blocker 5-hydroxydecanoate or Wortmannin as PI 3K/PDK-1 inhibitor. For Western blot, hearts were excised at five time points after xenon preconditioning (Control, 15, 25, 35, 45 min). Infarct size was reduced from 42 ± 6% (mean ± S.D.) to 27 ± 8% after xenon preconditioning ( P < 0.05). Western blot revealed an increased activation of PKC-ε after 45 min and of PDK-1 after 25 min during xenon preconditioning. 5-hydroxydecanoate and Wortmannin blocked both effects. PKC-ε is activated downstream of mitochondrial K ATP channels and PDK-1. Both pathways are functionally involved in xenon preconditioning.

Effects of the blockade of cardiac sarcolemmal ATP-sensitive potassium channels on arrhythmias and coronary flow in ischemia–reperfusion model in isolated rat hearts

Activation of ATP-sensitive K + channels (K ATP) during ischemia leads to arrhythmias and blockade of these channels exert antiarrhythmic action. In this study, we investigated the effects of HMR1098, a sarcolemmal K ATP channel blocker and 5-hydroxydeconoate (5-HD), a mitochondrial K ATP channel blocker on cardiac function and arrhythmias in isolated rat hearts. The hearts were subjected to 30 min coronary occlusion, followed by 30 min reperfusion. In the preischemic period, both HMR 1098 and 5-HD slightly increased coronary perfusion pressure. Coronary occlusion increased the perfusion pressure and decreased the left ventricular developed pressure (LVDP) in both control and drug-treated hearts. However, inhibition of LVDP was greater and recovery of the perfusion pressure was lower in 30 μmol/l HMR1098 and 100 μmol/l 5-HD-treated hearts compared to control ( P < 0.05). HMR1098, at 3 μmol/l, but not at 30 μmol/l, significantly reduced the ratio of bigeminis, couplets and salvos ( P < 0.05). Ventricular tachycardia and ventricular fibrillation were not prevented by HMR1098, at both concentrations, and with 5-HD (100 μmol/l). These results suggest that blockade of sarcK ATP and mitoK ATP channels exert weak antiarrhythmic action, but reduce the recovery of coronary perfusion and contractile force, implying that both types of K ATP channels have beneficial role in the recovery of ischemic rat myocardium.

Endogenous hydrogen sulfide contributes to the cardioprotection by metabolic inhibition preconditioning in the rat ventricular myocytes

The possible role of hydrogen sulfide (H 2S) in cardioprotection was investigated in isolated rat ventricular myocytes exposed to severe metabolic inhibition (MI) in glucose-free buffer containing 2-deoxy-D-glucose (2-DOG), an inhibitor of glycolysis. Pretreatment (30 min) with NaHS (a H 2S donor) at concentrations of 10 −5 to 10 −4 mol/L caused a concentration related increase in cell viability and the ratio of rod-shaped cells. A time course study showed that NaHS-induced cardioprotection occurred in 2 time windows (~1 h and 16-28 h). To observe whether endogenous H 2S may be involved in the delayed cardioprotection response of IP, DL-propargylglycine (PAG) and β-cyano-L-alanine (BCA; two inhibitors of H 2S biosynthesis) were used. Both drugs significantly attenuated the cardioprotection produced by MI using cell viability, cellular injury index, and electrically-induced [Ca 2+] i transients as end-points. These data suggest that endogenous H 2S plays an important role in the cardioprotection following MI preconditioning. In an attempt to determine the mechanism of the cardioprotective effect of H 2S, we examined the effect of blocking K ATP channels with glibenclamide (a non-selective K ATP channel blocker), 5-hydroxydecanoic acid (5-HD, a mitochondrial K ATP blocker), and HMR-1098 (a sarcolemmal K ATP blocker). The cardioprotective effects of NaHS were significantly attenuated by glibenclamide and HMR-1098 treatment but not by 5-HD. Inhibition of NO production with L-NG nitroarginine methyl ester (L-NAME) also attenuated the cardioprotection of NaHS. In conclusion, our findings provide the first evidence that H 2S may protect the heart most probably by activating sarcolemmal K ATP channels and/or provoking NO release and the cardioprotective effects of metabolic ischemic preconditioning is, at least partially, mediated by endogenous H 2S.

Exogenous hydrogen sulfide (H2S) protects against regional myocardial ischemia–reperfusion injury

Hydrogen sulfide (H2S) is a gaseous mediator, produced by the metabolic pathways that regulate tissue concentrations of sulfur-containing amino acids. Recent studies indicate that endogenous or exogenous H2S exerts physiological effects in the cardiovascular system of vertebrates, possibly through modulation of K ATP channel opening. The present study was undertaken to examine the hypothesis that H2S is cytoprotective against myocardial ischemia-reperfusion injury and that this protective action is mediated by K ATP opening. Rat isolated hearts were Langendorff-perfused and underwent 30 min left main coronary artery occlusion and 120 min reperfusion. The resulting injury was assessed as infarct size, determined by tetrazolium staining. Treatment of hearts with the H2S-donor, NaHS, commencing 10 min prior to the onset of coronary occlusion and maintained until 10 min reperfusion, resulted in a concentration-dependent limitation of infarct size (control, 41.0 +/- 2.6% of risk zone; NaHS 0.1 microM, 33.9 +/- 2.1%, [0.05 > P < 0.1]; NaHS 1 microM, 20.2 +/- 2.1% [P < 0.01]). Pretreatment with the K ATP channel blockers glibenclamide 10 microM or sodium 5-hydroxydecanoate (5HD) 100 microM led to abrogation of the infarct-limiting effect of NaHS 1 microM (glibenclamide + NaHS 42.5 +/- 3.6%; 5HD + NaHS 44.7 +/- 2.2%). No statistically significant effects of NaHS treatment on coronary flow, heart rate or left ventricular developed pressure were observed in this experimental preparation. These data provide the first evidence that exogenous H2S protects against irreversible ischemia-reperfusion injury in myocardium and support the involvement of K ATP opening in the mechanism of action. Further work is required to elucidate the potential role of endogenous H2S as a cytoprotective mediator against myocardial ischemia-reperfusion injury, the mechanisms regulating its generation, and the nature of its interaction with protein targets such as the K ATP channel.

5-HT uptake blockade prevents the increasing effect of K ATP channel blockers on electrically evoked [ 3H]-5-HT release in rat and mouse neocortical slices

To explore if prolonged – as opposed to acute – 5-HT uptake blockade can lead to changes in the function of ATP-dependent potassium (K ATP) channels, we investigated in rat and mouse neocortical slices the effects of K ATP channel blockers on electrically evoked [ 3H]-serotonin ([ 3H]-5-HT) release after short- and long-term exposure to 5-HT uptake blockers. Glibenclamide (1 μM), a K ATP channel blocker, enhanced the electrically evoked [ 3H]-5-HT release by 66 and by 77%, respectively, in rat and in mouse neocortex slices. This effect was confirmed in the rat by tolbutamide (1 μM), another K ATP channel antagonist. After short-term blockade (45 min) of 5-HT uptake, glibenclamide still increased the release of [ 3H]-5-HT in the rat. Glibenclamide, however, failed to enhance [ 3H]-5-HT release after long-term uptake blockade (210 min). In the mouse, however, both short- and long-term inhibition of 5-HT reuptake by citalopram (1 μM) prevented the facilitatory effect of glibenclamide. The Na +/K +-ATPase inhibitor ouabain (3.2 μM) abolished the glibenclamide-induced increase in [ 3H]-5-HT release in both rat and mouse, suggesting that an operative Na +/K +-ATPase is a prerequisite for activation of K ATP channels. The terminal 5-HT 1B autoreceptor-mediated feedback control was involved in the glibenclamide-induced increase in [ 3H]-5-HT release only in mouse neocortical tissue, as evident from the use of the 5-HT 1B autoreceptor ligands metitepin (1 μM) and cyanopindolol (1 μM). These results suggest that in the rat long-term uptake blockade leads to an impaired activity of the Na +/K +-ATPase, which increases intracellular ATP and consequently closes K ATP channels. In the mouse, however, short-term uptake blockade seems to already reduce the activity of the Na +/K +-ATPase and thereby the consumption of ATP. Blockade of 5-HT transporters thus may close K ATP channels through increased intracellular ATP. The following slight depolarisation seems to facilitate 5-HT release. These results may contribute to a better understanding of the mechanisms involved in the clinical time latency of antidepressant efficacy of monoamine uptake blockers.

The regulation of rotenone-induced inflammatory factor production by ATP-sensitive potassium channel expressed in BV-2 cells

Our previous studies have demonstrated that activating ATP-sensitive potassium channel (K ATP channel), not only improved Parkinsonian behavior and neurochemical symptoms, but also reduced iNOS activity and mRNA levels in striatum and nigra of rotenone rat model of Parkinson's disease (PD). In this study, it was first shown that the subunits of K ATP channels are expressed in BV-2 cells, and then it was investigated whether K ATP channel was involved in regulating inflammatory factor production from BV-2 cells activated by rotenone. It was found that K ATP channel was expressed in BV-2 cell and formed by the combination of Kir 6.1 and SUR 2A/2B. K ATP channel openers (KCOs) including pinacidil, diazoxide and iptakalim (Ipt) exerted beneficial effects on rotenone-induced morphological alterations of BV-2 cells, decreased tumor necrosis factor alpha (TNF-alpha) production and the expression and activity of inducible isoform of nitric oxide synthase (iNOS). Either glibenclamide or 5-hydroxydecanoate acid (a selective mitochondrial K ATP channel blocker) could abolish the effects of KCOs, suggesting that K ATP channels, especially mitochondrial ATP-sensitive potassium channels (mitoK ATP channels), played a crucial role in preventing the activation of BV-2 cells, and subsequently the production of a variety of proinflammatory factors. Therefore, activation of K ATP channel might be a new therapeutic strategy for treating neuroinflammatory and neurodegenerative disorders.

A role of opening of mitochondrial ATP-sensitive potassium channels in the infarct size-limiting effect of ischemic preconditioning via activation of protein kinase C in the canine heart

The opening of mitochondrial ATP-sensitive K + (mitoK ATP) channels triggers or mediates the infarct size (IS)-limiting effect of ischemic preconditioning (IP). Because ecto-5′-nucleotidase related to IP is activated by PKC, we tested whether the opening of mitoK ATP channels activates PKC and contributes to either activation of ecto-5′-nucleotidase or IS-limiting effect. In dogs, IP procedure decreased IS and activated ecto-5′-nucleotidase, both of which were mimicked by transient exposure to either cromakalim or diazoxide, and these effects were blunted by either GF109203X (a PKC inhibitor) or 5-hydroxydecanoate (a mitoK ATP channel blocker), but not by HMR-1098 (a surface sarcolenmal K ATP channel blocker). Either cromakalim or diazoxide activated both PKC and ecto-5′-nucleotidase, which was blunted by either GF109203X or 5-hydroxydecanoate, but not by HMR-1098. We concluded that the opening of mitoK ATP channels contributes to either activation of ecto-5′-nucleotidase or the infarct size-limiting effect via activation of PKC in canine hearts.

Isoflurane preconditioning protects motor neurons from spinal cord ischemia: Its dose–response effects and activation of mitochondrial adenosine triphosphate-dependent potassium channel

We examined in a rabbit model of transient spinal cord ischemia (SCI) whether isoflurane (Iso) preconditioning induces ischemic tolerance to SCI in a dose–response manner, and whether this effect is dependent on mitochondrial adenosine triphosphate-dependent potassium (K ATP) channel. Eighty-six rabbits were randomly assigned to 10 groups: Control group ( n = 8) received no pretreatment. Ischemic preconditioning (IPC) group ( n = 8) received 5 min of IPC 30 min before SCI. The Iso 1, Iso 2 and Iso 3 groups ( n = 10, 9, 8) underwent 30 min of 1.05, 2.1 and 3.15% Iso inhalation commencing 45 min before SCI. The Iso 1HD, Iso 2HD and Iso 3HD groups ( n = 9, 9, 8) each received a specific mitochondrial K ATP channel blocker, 5-hydroxydecanoic acid (5HD, 20 mg/kg), 5 min before each respective Iso inhalation. The 5HD group ( n = 8) received 5HD without Iso inhalation. The sham group ( n = 9) had no SCI. SCI was produced by infra-renal aortic occlusion via the inflated balloon of a Swan–Ganz catheter for 20 min. The Iso 1, Iso 2 and Iso 3 groups showed a better neurologic outcome and more viable motor nerve cells (VMNCs) in the anterior spinal cord 72 h after reperfusion than the control group ( p < 0.05). Iso 3 group showed a better neurologic outcome and more VMNCs than Iso 1 group ( p < 0.05). And, the Iso 1, Iso 2 and Iso 3 groups showed a better neurologic outcome and higher VMNC numbers than the corresponding Iso 1HD, Iso 2HD and Iso 3HD groups ( p < 0.05). This study demonstrates that Iso preconditioning protects the spinal cord against neuronal damage due to SCI in a dose–response manner via the activation of mitochondrial K ATP channels.

Is the sarcolemmal or mitochondrial K ATP channel activation important in the antiarrhythmic and cardioprotective effects during acute ischemia/reperfusion in the intact anesthetized rabbit model?

The relative contributions of cardiomyocyte sarcolemmal ATP-sensitive K + (K ATP) and mitochondrial K ATP channels in the cardioprotection and antiarrhythmic activity induced by K ATP channel openers remain obscure, though the mitochondrial K ATP channels have been proposed to be involved as a subcellular mediator in cardioprotection afforded by ischemic preconditioning. In the present study, we sought to investigate the effects of administration of ATP-sensitive K + channel (K ATP) openers (nicorandil and minoxidil), a specific mitochondrial K ATP channel blocker (5-hydroxydecanoate (5-HD)) and a specific sarcolemmal K ATP channel blocker (HMR 1883; (1-[5-[2-(5-chloro- o-anisamido)ethyl]-2-methoxyphenyl]sulfonyl-3-methylthiourea) prior to coronary occlusion as well as prior to post-ischemic reperfusion on survival rate, ischemia-induced and reperfusion-induced arrhythmias and myocardial infarct size in anesthetized albino rabbits. The thorax was opened in the left 4th intercostal space and after pericardiotomy the heart was exposed. In Group I ( n = 88), occlusion of the left main coronary artery and hence, myocardial ischemia-induced arrhythmias was achieved by tightening a previously placed loose silk ligature for 30 min. In Group II ( n = 206), arrhythmias were induced by reperfusion following a 20-min ligation of the left main coronary artery. Both in Group I and Group II, intravenous (i.v.) administration of nicorandil (0.47 mg/kg), minoxidil (0.5 mg/kg), HMR 1883 (3 mg/kg)/nicorandil and HMR 1883 (3 mg/kg)/minoxidil before coronary artery occlusion increased survival rate (86%, 75%, 75% and 86% vs. 55% in the control subgroup in Group I; 75%, 67%, 67% and 75% vs. 46% in the control subgroup in Group II), significantly decreased the incidence and severity of life-threatening arrhythmias. In Group II, i.v. administration of nicorandil and minoxidil before coronary artery occlusion significantly decreased myocardial infarct size. However, i.v. administration of nicorandil or minoxidil before reperfusion did neither increase survival rate nor confer any antiarrhythmic or cardioprotective effects. The antiarrhythmic and cardioprotective effects of both nicorandil and minoxidil were abolished by pretreating the rabbits with 5-HD (5 mg/kg, i.v. bolus), a selective mitochondrial K ATP channel blocker but not by HMR 1883 (3 mg/kg). In the present study, higher levels of malondialdehyde (MDA) and lower levels of reduced glutathione (GSH) and superoxide dismutase (SOD) in necrotic zone of myocardium in all the 16 subgroups in Group II suggest little anti-free radical property of nicorandil and minoxidil. We conclude that intervention by intravenous administration of nicorandil and minoxidil (through the selective activation of mitochondrial K ATP channels) increased survival rate and exhibited antiarrhythmic and cardioprotective effects during coronary occlusion and reperfusion in anesthetized rabbits when administered prior to coronary occlusion. The cardiomyocyte mitochondrial K ATP channel may be a pharmacologically modulable target of cardioprotection and antiarrhythmic activity.

Iptakalim hydrochloride protects cells against neurotoxin-induced glutamate transporter dysfunction in in vitro and in vivo models

Iptakalim hydrochloride (Ipt), a novel antihypertensive drug, exhibits K ATP channel activation. Here, we report that Ipt remarkably protects cells against neurotoxin-induced glutamate transporter dysfunction in in vitro and in vivo models. Chronic exposure of cultured PC12 cells to neurotoxins, such as 6-OHDA, MPP +, or rotenone, decreased overall [ 3H]-glutamate uptake in a concentration-dependent manner. Pre-treatment using 10 μM Ipt significantly protected cells against neurotoxin-induced glutamate uptake diminishment, and this protection was abolished by the K ATP channel blocker glibenclamide (20 μM), suggesting that the protective mechanisms may involve the opening of K ATP channels. In 6-OHDA-treated rats (as an in vivo Parkinson's disease model), [ 3H]-glutamate uptake was significantly lower in synaptosomes isolated from the striatum and cerebral cortex, but not the hippocampus. Pre-conditioning using 10, 50, and 100 μM Ipt significantly restored glutamate uptake impairment and these protections were abolished by blockade of K ATP channels. It is concluded that Ipt exhibits substantial protection of cells against neurotoxicity in in vitro and in vivo models. The cellular mechanisms of this protective effect may involve the opening of K ATP channels. Collectively, Ipt may serve as a novel and effective drug for PD therapy.

Effects of ATP-sensitive potassium channel activators diazoxide and BMS-191095 on membrane potential and reactive oxygen species production in isolated piglet mitochondria

Mitochondrial ATP-sensitive potassium (mitoK ATP) channel openers protect the piglet brain against ischemic stress. Effects of mitoK ATP channel agonists on isolated mitochondria, however, have not been directly examined. We investigated the effects of K ATP channel openers and blockers on membrane potential and on the production of reactive oxygen species (ROS) in isolated piglet mitochondria. Diazoxide and BMS-191095, putative selective openers of mitoK ATP, decreased the mitochondrial membrane potential (Δ Ψ m). On a molar basis, diazoxide was less effective than BMS-191095. In contrast, diazoxide but not BMS-191095 increased ROS production by mitochondria. Since diazoxide also inhibits succinate dehydrogenase (SDH), we examined the effects of 3-nitropropionic acid (3-NPA), an inhibitor of SDH. 3-NPA failed to change the Δ Ψ m but increased ROS production. Inhibitors of K ATP channels did not affect resting Δ Ψ m or ROS production, but glibenclamide and 5-hydroxydecanoate (5-HD) blocked effects of diazoxide and BMS-191095 on Δ Ψ m and diazoxide effects on ROS production. We conclude that BMS-191095 has selective effects on mitoK ATP channels while diazoxide also increases ROS production probably via inhibition of SDH.

Intact nitric oxide production is obligatory for the sustained flow response during hypercapnic acidosis in guinea pig heart

The mechanisms underlying hypercapnic coronary dilation remain unsettled. This study tests the hypothesis that flow dependent NO production is obligatory for the hypercapnic flow response. In isolated, constant pressure (CP) perfused guinea pig hearts a step change of arterial pCO(2) from 38.6 to 61.4 mm Hg induced a bi-phasic flow response with an early transient (maximum 60 s) and a consecutive persisting flow rise (121.6+/-6.6 (S.D.) % after 10 min). In contrast, when perfused with constant flow (CF), perfusion pressure only transiently (2 min) fell by 7.4+/-4.8 % following the step change of arterial pCO(2). In CP perfused hearts L-NAME (100 micromol/l) specifically abolished the delayed flow rise during hypercapnic acidosis (102.37+/-2.9% after 10 min), whereas the inhibitor had no effect on perfusion pressure response in CF perfused hearts. Under CP perfusion arterial hypercapnia resulted in a transient rise of coronary cGMP release (from 0.69+/-0.35 to 1.12+/-0.68 pmol/ml), which was abolished after L-NAME. Surprisingly, the K(+)ATP channel blocker glibenclamide did not have any significant effect on the hypercapnic flow response but largely blunted reactive hyperemia after a 20 s flow stop. The delayed steady state hypercapnic flow response in guinea pig heart requires intact NO production. The absence of a persisting decrease in coronary resistance under CF perfusion points to an important role of shear stress dependent NO production.

Alterations of insulin secretion following long-term manipulation of ATP-sensitive potassium channels by diazoxide and nateglinide

Previous studies have shown that prolonged exposure to drugs, which act via blocking K ATP channels, can desensitize the insulinotropic effects of drugs and nutrients acting via K ATP channels. In this study, effects of prolonged exposure to diazoxide, a K ATP channel opener, on beta cell function were examined using clonal BRIN-BD11 cells. The findings were compared to the long-term effects of K ATP channel blockers nateglinide and tolbutamide. Following 18 h exposure to 200 μM diazoxide, the amounts of insulin secreted in response to glucose, amino acids and insulinotropic drugs were increased. Secretory responsiveness to a variety of agents acting via K ATP channels was retained following prolonged diazoxide exposure. In contrast, 18 h exposure to 100 μM nateglinide significantly attenuated the insulin secretory responses to tolbutamide, nateglinide and BTS 67 582. Glucose- and l-alanine-stimulated insulin release were unaffected by prolonged nateglinide exposure, however responsiveness to l-leucine and l-arginine was diminished. Prolonged exposure to nateglinide had no effect on forskolin- and PMA-stimulated insulin release, and the overall pattern of desensitization was similar to that induced by 100 μM tolbutamide. We conclude that in contrast to chronic long-term K ATP channel blockade, long-term diazoxide treatment is not harmful to K ATP channel mediated insulin secretion and may have beneficial protective effects on beta cell function.

Responses to bradykinin are mediated by NO-independent mechanisms in the rat hindlimb vascular bed

The vasodilator response to bradykinin (BK) appears to be mediated by a number of different endothelium-derived relaxing factors (EDRFs). The EDRFs mediating the response depend on the species and vascular bed studied. The mechanism by which BK dilates the hindlimb vascular bed was investigated in the anesthetized rat. BK produced dose-dependent increases hindlimb blood flow. The NOS antagonist L-NAME had little effect on the magnitude of the increase in flow when baseline hemodynamic parameters were corrected by an NO donor infusion. However, the duration of the response was slightly shortened by L-NAME. Charybdotoxin (Chtx) and apamin nearly abolished the L-NAME resistant component of the hindlimb vasodilator response to BK, but did not affect the hindlimb vasodilator response to the sodium nitroprusside (SNP). The cyclooxygenase inhibitor meclofenamate and the K +-ATP channel blocker U37883A, in the presence of L-NAME, did not alter the vasodilator response to BK. These results suggest that a significant portion of the hindlimb vasodilator response to BK is mediated by the activation of K Ca channels, and independent of NO synthesis, cyclooxygenase products, and activation of K +-ATP channels. The present data suggest that the mechanisms mediating the vasodilator response to BK in the hindlimb vascular bed of the rat are complex, consisting of a Chtx and apamin sensitive, L-NAME resistant phase and a minor phase mediated by NO. In contrast, NO accounts for about half of the hindlimb vasodilator response to acetylcholine (ACh), with the other half of the response mediated by a Chtx and apamin sensitive mechanism. Additionally, the present results demonstrate that the NO donor infusion technique is able to compensate for the loss of basal NO production following inhibition of NOS, and to restore hemodynamic parameters to pre-L-NAME levels, making it a useful technique for the investigation of the role of NO in mediating vascular responses.

HMR1402, a potassium ATP channel blocker during hyperdynamic porcine endotoxemia: effects on hepato-splanchnic oxygen exchange and metabolism

To assess the effects of the potassium ATP (KATP) channel blocker HMR1402 (HMR) on systemic and hepato-splanchnic hemodynamics, oxygen exchange and metabolism during hyperdynamic porcine endotoxemia. Prospective, randomized, controlled study with repeated measures. SETTING. Animal laboratory. Eighteen pigs allocated to receive endotoxin alone (control group, CON, n=10) or endotoxin and HMR (6 mg/kg h(-1), n=8). Anesthetized, mechanically ventilated, and instrumented pigs receiving continuous i.v. endotoxin were resuscitated with hetastarch to maintain mean arterial pressure (MAP) >60 mmHg. Twelve hours after starting the endotoxin infusion, they received HMR or its vehicle for another 12 h. HMR transiently increased MAP by about 15 mmHg, but this effect was only present during the first 1 h of infusion. The HMR decreased cardiac output due to a fall in heart rate, and thereby reduced liver blood flow. While liver O(2) delivery and uptake remained unchanged, HMR induced hyperlactatemia [from 1.5 (1.1; 2.0), 1.4 (1.2; 1.8), and 1.2 (0.8; 2.0) to 3.1 (1.4; 3.2), 3.2 (1.6; 6.5), and 3.0 (1.0; 5.5) mmol/l in the arterial, portal and hepatic venous samples, respectively] and further increased arterial [from 8 (3; 13) to 23 (11; 57); p<0.05], portal [from 9 (4; 14) to 23 (14; 39); p<0.05] and hepatic vein [from 7 (0; 15) to 30 (8; 174), p<0.05] lactate/pyruvate ratios indicating impaired cytosolic redox state. The short-term beneficial hemodynamic effects of KATP channel blockers have to be weighted with the detrimental effect on mitochondrial respiration.