Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0022116 (ischemia)
 91,303 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cromakalim, an adenosine triphosphate-sensitive potassium channel opener, shows proarrhythmic activity at moderate doses (1-10 micromol/liter) in the ischemic and reperfused myocardium. We studied the effects of extracellular Mg++ ([Mg++]o) on the incidence of reperfusion-induced ventricular fibrillation and ventricular tachycardia in isolated working hearts (n = 12 in each group) subjected to 20 min of global ischemia followed by 30 min of reperfusion, a model eliciting a low incidence of reperfusion arrhythmias, obtained from 8-wk streptozotocin-induced diabetic rats. Cromakalim, at a concentration of 3 micromol/liter, perfused 5 min before the induction of ischemia and throughout reperfusion increased the incidence of ventricular fibrillation and ventricular tachycardia from their drug-free diabetic control values of 25 and 42% ([Mg++]o = 1.2 mmol/liter) to 92% (P < .05) and 100% (P < .05), respectively. Glibenclamide at a concentration of 3 micromol/liter prevented the proarrhythmiac activity of cromakalim. Increasing concentration of [Mg++]o to 2.4, 3.6 and 4.8 mmol/liter in the perfusion buffer, the arrhythmogenic effect of cromakalim was also abolished. Thus, with 2.4, 3.6 and 4.8 mmol/liter of [Mg++]o perfused before the administration of cromakalim and the onset of ischemia, the incidence of reperfusion-induced ventricular tachycardia was reduced from 92% (in cromakalim treated group) to 67%, 42% (P < .05), and 25% (P < .05), respectively. The incidence of reperfusion-induced ventricular tachycardia showed the same pattern. Elevated [Mg++]o prevented the cromakalim-induced cellular Na+ gain and K+ loss, measured by atomic absorption spectrophotometer. [Mg++]o could prevent the proarrhythmic activity of cromakalim, and the use of cromakalim as an antihypertensive or antiischemic agent may be of particular concern in the population of postischemic diabetic subjects who are known to be at high risk of sudden coronary death.
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PMID:Extracellular Mg++ manipulation prevents the proarrhythmic activity of cromakalim in ischemic/reperfused diabetic hearts. 922 69

Previous studies showed a poor correlation between sarcolemmal K+ currents and cardioprotection for ATP-sensitive K+ channel (KATP) openers. Diazoxide is a weak cardiac sarcolemmal KATP opener, but it is a potent opener of mitochondrial KATP, making it a useful tool for determining the importance of this mitochondrial site. In reconstituted bovine heart KATP, diazoxide opened mitochondrial KATP with a K1/2 of 0.8 mumol/L while being 1000-fold less potent at opening sarcolemmal KATP. To compare cardioprotective potency, diazoxide or cromakalim was given to isolated rat hearts subjected to 25 minutes of global ischemia and 30 minutes of reperfusion. Diazoxide and cromakalim increased the time to onset of contracture with a similar potency (EC25, 11.0 and 8.8 mumol/L, respectively) and improved postischemic functional recovery in a glibenclamide (glyburide)-reversible manner. In addition, sodium 5-hydroxydecanoic acid completely abolished the protective effect of diazoxide. While-myocyte studies showed that diazoxide was significantly less potent than cromakalim in increasing sarcolemmal K+ currents. Diazoxide shortened ischemic action potential duration significantly less than cromakalim at equicardioprotective concentrations. We also determined the effects of cromakalim and diazoxide on reconstituted rat mitochondrial cardiac KATP activity. Cromakalim and diazoxide were both potent activators of K+ flux in this preparation (K1/2 values, 1.1 +/- 0.1 and 0.49 +/- 0.05 mumol/L, respectively). Both glibenclamide and sodium 5-hydroxydecanoic acid inhibited K+ flux through the diazoxide-opened mitochondrial KATP. The profile of activity of diazoxide (and perhaps KATP openers in general) suggests that they protect ischemic hearts in a manner that is consistent with an interaction with mitochondrial KATP.
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PMID:Cardioprotective effect of diazoxide and its interaction with mitochondrial ATP-sensitive K+ channels. Possible mechanism of cardioprotection. 940 Mar 89

The objectives of the present study were to determine the localization of K(ATP) channels in normal retina and to evaluate their potential roles in ischemic preconditioning (IPC) in a rat model of ischemia induced by increased intraocular pressure (IOP). Brown Norway rats were subjected to sublethal 3-, lethal 20- and 40-min ischemia and the functional recovery was evaluated using electroretinography. The time interval between ischemic insults ranged from 1 to 72 h. The effects of K(ATP) channel blockade on IPC protection were studied by treatment with 0.01% glipizide. IPC was mimicked by injection of K(ATP) channel openers of 0.01% (-)cromakalim or 0.01% P1060 72 h before 20-min ischemia. Co-expression of K(ATP) channel subunits Kir6.2/SUR1 was observed in the retinal pigment epithelium, inner segments of photoreceptors, outer plexiform and ganglion cell layers and at the border of the inner nuclear layer. In contrast to a 20- or 40-min ischemia, a 3-min ischemia induced no alteration of the electroretinogram (ERG) and constituted the preconditioning stimulus. An ischemic challenge of 40 min in preconditioned rats induced impairment of retinal function. However, animals preconditioned 24, 48 and 72 h before 20-min ischemia had a significant improvement of the ERG. (-)Cromakalim and P1060 mimicked the effect of IPC. Glipizide significantly suppressed the protective effects of preconditioning. In conclusion, activation of K(ATP) channels plays an important role in the mechanism of preconditioning by enhancing the resistance of the retina against a severe ischemic insult.
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PMID:ATP-sensitive potassium channels (K(ATP)) in retina: a key role for delayed ischemic tolerance. 1116 74

Cardioprotection by K(ATP) channel openers during ischemia is well documented although ill understood. Proarrhythmic effects may be an important drawback. K(ATP) channel modulation influences neurotransmitter release during ischemia in brain synaptosomes. Therefore, we studied the effects of K(ATP) channel modulation on myocardial noradrenaline release and arrhythmias in ischemic rabbit hearts. Isolated rabbit hearts were perfused according to Langendorff and stimulated. Local electrograms were recorded and K+-selective electrodes were inserted in the left ventricular free wall. Cromakalim (3 microM) or glibenclamide (3 microM) was added 20 min prior to induction of global ischemia. After 15, 20, or 30 min of ischemia, hearts were reperfused and noradrenaline content of the first 100 ml of reperfusate was measured. Cromakalim (n = 16) prevented the second rise of extracellular [K(+)] in accordance with its cardioprotective effect. Cromakalim significantly reduced noradrenaline release after 15 min (mean, 169 +/- SEM 97 pmol/gr dry weight vs. control 941 +/- 278; p < 0.05) and 20 min of ischemia (230 +/- 125 pmol/gr dry wt vs. control 1,460 +/- 433; p < 0.05), but after 30 min of ischemia, the difference in noradrenaline release was no longer significant (cromakalim 2,703 +/- 1,195 pmol/gr dry wt vs. control 5,413 +/- 1,310; p = 0.08). Ventricular fibrillation or ventricular tachycardia occurred in 10 of 13 control hearts (77%) (n = 19), in six of 10 glibenclamide-treated hearts (60%) (n = 15), and in six of 14 cromakalim-treated hearts (43%) (p = NS). Cromakalim significantly accelerated onset of ventricular tachycardia or fibrillation (mean +/- SEM onset after 12.5 +/- 1.6 min ischemia vs. control 16.2 +/- 0.7 min; p < 0.05). Noradrenaline release occurred only in cromakalim-treated hearts with early-onset arrhythmias whereas no noradrenaline release was observed in cromakalim-treated hearts without ventricular tachycardia or fibrillation. Our results show that activation of the K(ATP) channel by cromakalim during ischemia reduces myocardial noradrenaline release and postpones the onset of irreversible damage, contributing to the cardioprotective potential of K(ATP) openers during myocardial ischemia.
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PMID:K(ATP) channel opening during ischemia: effects on myocardial noradrenaline release and ventricular arrhythmias. 1148 45

We studied changes in arteriolar and venular diameters and macromolecular leakage altered by ischemia/reperfusion (I/R) and topically applied histamine after I/R and how these changes were modulated by cromakalim (KATP-channel opener) and glibenclamide (KATP-channel blocker). Golden hamsters were prepared for intravital microscopy of the cheek pouch. Ischemia was induced by an inflatable silicon rubber cuff mounted around the neck of the cheek pouch prepared for intravital microscopy. Saline, histamine, cromakalim, and glibenclamide were applied in the superfusion solution. FITC-dextran was injected i.v. 30 min before initiation of ischemia as a marker of macromolecular leakage. Cromakalim 10(-6) M, but not 10(-8) M, caused arteriolar dilation in ischemic and normal (nonischemic) preparations, and glibenclamide, 10 -10) M and 10(-8) M, had no effects on vessel diameters. Application of cromakalim 10(-6) M increased arteriolar diameter (+54%) and macromolecular leakage in normal and nonischemic cheek pouches and had an additive effect on macromolecular leakage in ischemic (I/R) preparations but had no effect on histamine-induced increase in macromolecular leakage. Glibenclamide, 10(-10) M and 10(-8) M, inhibited I/R-induced but not histamine-induced increases in macromolecular leakage. We concluded that cromakalim may increase macromolecular leakage. This effect is additive to I/R-induced leakage suggesting that stimulation of KATP-channels could take part in the regulation of macromolecular leakage in postcapillary venules. The KATP-blocker glibenclamide inhibited I/R-induced but not histamine-induced macromolecular leakage at concentrations that had no constricting effect on arterioles, and therefore, it cannot be excluded that glibenclamide reduced plasma leakage by some unknown mechanism.
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PMID:Effects of cromakalim and glibenclamide on arteriolar and venular diameters and macromolecular leakage in the microcirculation during ischemia/reperfusion. 1186 12

We have shown previously that flow-adapted endothelial cells respond to cessation of flow with cell membrane depolarization and increased production of reactive oxygen species, resulting in activation of transcription factors and increased DNA synthesis. This study utilized flow cytometry to evaluate cellular proliferation with ischemia and to determine the role of reactive oxygen species and apoptosis. PKH26-labeled rat pulmonary microvascular endothelial cells were seeded in an artificial capillary system and subjected to flow at 5 dynes/cm(2) for 96 h or for 72 h followed by 24 h of simulated "ischemia." Ischemia resulted in a 2.5-fold increase in the cellular proliferation index. Cell-cycle analysis showed G0/G1 arrest and decreased S plus G2/M during flow adaptation, whereas ischemia resulted in a three-fold increase of cells in S plus G2/M phases. Apoptotic cells as detected by TUNEL and annexin V binding assays were ~5% of total cells with no differences between static, flow-adapted, and "ischemic" groups. Reactive oxygen species production during a 1-h period following onset of ischemia was confirmed by oxidation of the fluorophore, dichlorofluorescein, and was inhibited by cromakalim, a K(ATP) channel agonist, or diphenyleneiodonium, a flavoprotein inhibitor. Cromakalim and diphenyleneiodonium also markedly inhibited cell proliferation in the flow-adapted ischemic cells, but had no effect on subconfluent cells cultured under static conditions. These results indicate reactive oxygen species-dependent endothelial cell proliferation in flow-adapted microvascular endothelial cells as a response to ischemia and indicate that this response is not a consequence of apoptosis.
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PMID:Endothelial cell proliferation associated with abrupt reduction in shear stress is dependent on reactive oxygen species. 1502 26

Loss of fluid shear stress (ischemia) to the lung endothelium causes endothelial plasma membrane depolarization via ATP-sensitive K(+) (K(ATP)) channel closure, initiating a signaling cascade that leads to NADPH oxidase (NOX2) activation and ROS production. Since wortmannin treatment significantly reduces ROS production with ischemia, we investigated the role of phosphoinositide 3-kinase (PI3K) in shear-associated signaling. Pulmonary microvascular endothelial cells in perfused lungs subjected to abrupt stop of flow showed membrane depolarization and ROS generation. Stop of flow in flow-adapted mouse pulmonary microvascular endothelial cells in vitro resulted in the activation of PI3K and Akt as well as ROS generation. ROS generation in the lungs in situ was almost abolished by the PI3K inhibitor wortmannin and the PKC inhibitor H7. The combination of the two (wortmannin and H7) did not have a greater effect. Activation of NOX2 was greatly diminished by wortmannin, knockout of Akt1, or dominant negative PI3K, whereas membrane depolarization was unaffected. Ischemia-induced Akt activation (phosphorylation) was not observed with K(ATP) channel-null cells, which showed minimal changes in membrane potential with ischemia. Activation of Akt was similar to wild-type cells in NOX2-null cells, which do not generate ROS with ischemia. Cromakalim, a K(ATP) channel agonist, prevented both membrane depolarization and Akt phosphorylation with ischemia. Thus, Akt1 phosphorylation follows cell membrane depolarization and precedes the activation of NOX2. These results indicate that PI3K/Akt and PKC serve as mediators between endothelial cell membrane depolarization and NOX2 assembly.
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PMID:Membrane depolarization is the trigger for PI3K/Akt activation and leads to the generation of ROS. 2200 59


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