[Diazoxide administered to control hypertension in patients on extracorporeal hemodialysis (author's transl)].
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Adolescent↗
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Results for “DIAZOXIDE”
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Life-threatening pancytopenia associated with diazoxide.
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Letter↗
Diazoxide, glipizide, hypertension and hypoglycaemia.
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Adult↗
[Clinical and experimental studies on the effect of benzothiadiazine (diazoxide) on the carbohydrate metabolism].
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Adolescent↗
Role of protein kinase C in mitochondrial KATP channel-mediated protection against Ca2+ overload injury in rat myocardium.
Growing evidence exists that ATP-sensitive mitochondrial potassium channels (MitoKATP channel) are a major contributor to the cardiac protection against ischemia. Given the importance of mitochondria in the cardiac cell, we tested whether the potent and specific opener of the MitoKATP channel diazoxide attenuates the lethal injury associated with Ca2+overload. The specific aims of this study were to test whether protection by diazoxide is mediated by MitoKATP channels; whether diazoxide mimics the effects of Ca2+ preconditioning; and whether diazoxide reduces Ca2+ paradox (PD) injury via protein kinase C (PKC) signaling pathways. Langendorff-perfused rat hearts were subjected to the Ca2+ PD (10 minutes of Ca2+ depletion followed by 10 minutes of Ca2+ repletion). The effects of the MitoKATP channel and other interventions on functional, biochemical, and pathological changes in hearts subjected to Ca2+ PD were assessed. In hearts treated with 80 micromol/L diazoxide, left ventricular end-diastolic pressure and coronary flow were significantly preserved after Ca2+ PD; peak lactate dehydrogenase release was also significantly decreased, although ATP content was less depleted. The cellular structures were well preserved, including mitochondria and intercalated disks in diazoxide-treated hearts compared with nontreated Ca2+ PD hearts. The salutary effects of diazoxide on the Ca2+ PD injury were similar to those in hearts that underwent Ca2+ preconditioning or pretreatment with phorbol 12-myristate 13-acetate before Ca2+ PD. The addition of sodium 5-hydroxydecanoate, a specific MitoKATP channel inhibitor, or chelerythrine chloride, a PKC inhibitor, during diazoxide pretreatment completely abolished the beneficial effects of diazoxide on the Ca2+ PD. Blockade of Ca2+ entry during diazoxide treatment by inhibiting L-type Ca2+ channel with verapamil or nifedipine also completely reversed the beneficial effects of diazoxide on the Ca2+ PD. PKC-delta was translocated to the mitochondria, intercalated disks, and nuclei of myocytes in diazoxide-pretreated hearts, and PKC-alpha and PKC-epsilon were translocated to sarcolemma and intercalated disks, respectively. This study suggests that the effect of the MitoKATP channel is mediated by PKC-mediated signaling pathway.
Adenosine Triphosphate↗
Activation of mitochondrial ATP-sensitive K(+) channel for cardiac protection against ischemic injury is dependent on protein kinase C activity.
Protein kinase C (PKC) is involved in the second messenger signaling cascade during ischemic and Ca(2+) preconditioning. Given that the pharmacological activation of mitochondrial ATP-sensitive K(+) (mitoK(ATP)) channels also mimics preconditioning, the mechanisms linking PKC activation and mitoK(ATP) channels remain to be established. We hypothesize that PKC activity is important for the opening of the mitoK(ATP) channel. To examine this, a specific opener of the mitoK(ATP) channel, diazoxide, was used in conjunction with subcellular distribution of PKC in a model of ischemia/reperfusion (I/R). Langendorff-perfused rat hearts were subjected to 40-minute ischemia followed by 30-minute reperfusion. Effects of activation of the mitoK(ATP) channel and other interventions on functional, biochemical, and pathological changes in ischemic hearts were assessed. In hearts treated with diazoxide, left ventricular end-diastolic pressure and coronary flow were significantly improved after I/R; lactate dehydrogenase release was also significantly decreased. The morphology was well preserved in diazoxide-treated hearts compared with nontreated ischemic control hearts. The salutary effects of diazoxide on the ischemic injury were similar to those of Ca(2+) preconditioning. Administration of sodium 5-hydroxydecanoate, an effective blocker of the mitoK(ATP) channel, or chelerythrine or calphostin C, an inhibitor of PKC, during diazoxide pretreatment or during continuous presence of diazoxide in the ischemic period, completely abolished the beneficial effects of the diazoxide on the I/R injury. Blockade of Ca(2+) entry during diazoxide treatment by inhibiting the L-type Ca(2+) channel with verapamil also completely reversed the beneficial effect of diazoxide during I/R. PKC-alpha was translocated to sarcolemma, whereas PKC-delta was translocated to the mitochondria and intercalated disc, and PKC-epsilon was translocated to the intercalated disc of the diazoxide-pretreated hearts. Colocalization studies for mitochondrial distribution with tetramethylrhodamine ethyl ester (TMRE) and PKC isoforms by immunoconfocal microscopy revealed that PKC-delta antibody specifically stained the mitochondria. ATP was significantly increased in the diazoxide-treated hearts. Moreover, the data suggest that activation and translocation of PKC to mitochondria appear to be important for the protection mediated by mitoK(ATP) channel.
Adenosine Triphosphate↗
Opening of mitochondrial K(ATP) channels triggers the preconditioned state by generating free radicals.
The critical time for opening mitochondrial (mito) K(ATP) channels, putative end effectors of ischemic preconditioning (PC), was examined. In isolated rabbit hearts 29+/-3% of risk zone infarcted after 30 minutes of regional ischemia. Ischemic PC or 5-minute exposure to 10 micromol/L diazoxide, a mito K(ATP) channel opener, reduced infarction to 3+/-1% and 8+/-1%, respectively. The mito K(ATP) channel closer 5-hydroxydecanoate (200 micromol/L), bracketing either 5-minute PC ischemia or diazoxide infusion, blocked protection (24+/-3 and 28+/-6% infarction, respectively). However, 5-hydroxydecanoate starting 5 minutes before long ischemia did not affect protection. Glibenclamide (5 micromol/L), another K(ATP) channel closer, blocked the protection by PC only when administered early. These data suggest that K(ATP) channel opening triggers protection but is not the final step. Five minutes of diazoxide followed by a 30-minute washout still reduced infarct size (8+/-3%), implying memory as seen with other PC triggers. The protection by diazoxide was not blocked by 5 micromol/L chelerythrine, a protein kinase C antagonist, given either to bracket diazoxide infusion or just before the index ischemia. Bracketing preischemic exposure to diazoxide with 50 micromol/L genistein, a tyrosine kinase antagonist, did not affect infarction, but genistein blocked the protection by diazoxide when administered shortly before the index ischemia. Thus, although it is not protein kinase C-dependent, the protection by diazoxide involves tyrosine kinase. Bracketing diazoxide perfusion with N:-(2-mercaptopropionyl) glycine (300 micromol/L) or Mn(III)tetrakis(4-benzoic acid) porphyrin chloride (7 micromol/L), each of which is a free radical scavenger, blocked protection, indicating that diazoxide triggers protection through free radicals. Therefore, mito K(ATP) channels are not the end effectors of protection, but rather their opening before ischemia generates free radicals that trigger entrance into a preconditioned state and activation of kinases.
Adenosine Triphosphate↗
[Effect of opening of mitochondrial ATP-sensitive K⁺ channel on the distribution of cytochrome C and on proliferation of human pulmonary arterial smooth muscle cells in hypoxia].
The objective of this paper was to investigate the contribution of mitochondrial ATP-sensitive K+ channel (mitoK(ATP)) and mitochondrial membrane potential (Deltapsim) to the distribution of cytochrome C in human pulmonary arterial smooth muscle cells (HPASMCs) and to the proliferation of HPASMCs induced by hypoxia. HPASMCs were divided into 6 groups, as following: (1) control group: cultured under normoxia; (2) diazoxide group: cultured in normoxia with diazoxide, an opener of mitoK(ATP); (3) 5-HD group: cultured in normoxia with 5-hydroxydecanoate (5-HD), an antagonist of mitoK(ATP); (4) 24-hour hypoxia group: cultured in hypoxia for 24 h; (5) 24-hour hypoxia + diazoxide group: cultured in hypoxia with diazoxide for 24 h; (6) 24-hour hypoxia + 5-HD group: cultured in hypoxia with 5-HD for 24 h. The relative changes in mitochondrial potential were tested with rhodamine fluorescence (R-123) technique. Western blot was used to detect the expression of cytochrome C protein in cell plasma and mitochondria,respectively. The expression of cell caspase-9 protein was determined with Western blot. The proliferation of HPASMCs was examined by cell cycle analysis and MTT colorimetric assay. The results were as following: after exposure to diazoxide for 24 h, the intensity of R-123 fluorescence in normoxic HPASMCs was significantly increased compared with that in the control group (P<0.05), but there was no significant change of the intensity of R-123 fluorescence after the HPASMCs had been exposed to 5-HD for 24 h; 24-hour hypoxia or 24-hour hypoxia + diazoxide could markedly increase the intensity of R-123 fluorescence in HPASMCs compared with normoxia (P<0.05), and the change was more significant in 24-hour hypoxia + diazoxide group than that in 24-hour hypoxia group (P<0.05); 5-HD could weaken the effect of 24-hour hypoxia on the intensity of R-123 fluorescence. After exposure to diazoxide for 24 h, the ratio of the expression of cytosolic cytochrome C protein to that of mitochondrial cytochrome C protein was significantly decreased compared with that in the control group (P<0.05), and the expression of caspase-9 protein was significantly decreased compared with that in the control group (P<0.05). The percentage of S phase and A value of MTT were significantly increased compared with those in the control group (P<0.05). But there were no significant changes in these tests after HPASMCs had been exposed to 5-HD for 24 h (P>0.05). After exposure to hypoxia or hypoxia + diazoxide for 24 h, the ratio of the expression of cytosolic cytochrome C protein to that of mitochondrial cytochrome C protein and the expression of caspase-9 protein were significantly decreased compared with those in the control group (P<0.05). The percentage of S phase and A value of MTT were significantly increased compared with those in the control group (P<0.05). These changes were more significant in 24-hour hypoxia + diazoxide group than those in 24-hour hypoxia group (P<0.05). 5-HD could weaken the effect of hypoxia on the changes of the distribution of cytochrome C, the expression of caspase-9 in HPASMCs and the proliferation of HPASMCs induced by hypoxia (P<0.05). All these results suggest that the opening of mitoK(ATP) followed by a depolarization of Deltapsim induced by hypoxia might contribute to the inhibition of the release of cytochrome C from mitochondria to plasma in HPASMCs. This might be a mechanism of the development of hypoxic pulmonary hypertension. The signal transduction pathway of mitochondria might play an important role in the relationship between Deltapsim and apoptosis of HPASMCs.
Cell Hypoxia↗
MitoKATP channel activation suppresses gap junction permeability in the ischemic myocardium by an ERK-dependent mechanism.
BACKGROUND: Ischemic preconditioning accelerates suppression of gap junction (GJ) permeability during myocardial ischemia, and GJ blockers reduce infarct size. We hypothesized that the mitochondrial ATP-sensitive K+ (mitoKATP) channel is one of the mechanisms regulating GJ permeability through the mitogen-activated protein kinase ERK, leading to cardioprotection. METHODS AND RESULTS: In isolated rabbit hearts, tissues were sampled before and after infusion of diazoxide, a selective mitoKATP channel opener, and their intercalated disc-rich fractions were obtained for immunoblotting of mitogen-activated protein kinases. GJ permeability in the myocardium was assessed by using Lucifer yellow as a tracer of GJ communication. Infarction was induced by 30-min global ischemia/2 h reperfusion, and infarct size was expressed as a percent of area-at-risk (%IS/AR). Diazoxide (100 microM) induced phosphorylation of ERK1/2 and 279Ser/282Ser of connexin-43, a GJ subunit protein, and phospho-ERK1/2 was co-immunoprecipitated with connexin-43 in the diazoxide-treated myocardium. This ERK1/2 phosphorylation by diazoxide was inhibited by N-2-mercaptopropionyl-glycine, a free radical scavenger. Diazoxide at 10 and 100 microM reduced intercellular transport of Lucifer yellow during ischemia by 44% and 69%, respectively, and this effect of diazoxide on GJ communication was abolished by PD98059, an ERK inhibitor. Pretreatment with 10 microM and 100 microM diazoxide reduced %IS/AR from 57.1+/-3.7% to 21.5+/-10.5% and 5.0+/-1.3%, respectively. PD98059 abolished cardioprotection by 10 microM diazoxide but not that by 100 microM diazoxide. CONCLUSIONS: Opening of the mitoKATP channel activates ERK1/2 via free radicals and induces ERK-mediated suppression of GJ permeability. This suppression of GJ permeability may partly contribute to cardioprotection afforded by mitoKATP channel activation.
Adenosine Triphosphate↗
[Protective effect of mitochondrial ATP-sensitive potassium channel opener on rat heart during hypothermic preservation].
OBJECTIVE: To investigate whether the mitochondrial ATP-sensitive potassium channel (mitoK(ATP)) opener diazoxide as an additive to cardioplegia solution could enhance myocardial protection during hypothermic preservation of the rat heart. METHODS: The Langendorff model of isolated rat heart was used. After equilibrium, the hearts were stored in Celsior cardioplegia solution at 4 degree with or without supplement of diazoxide for 3 or 8 h followed by 60 minutes reperfusion. The recovery of cardiac contractile function, myocardial enzyme leakage in the coronary effluent, and myocardial water content were determined. The myocardial ultrastructure was also observed. RESULT: (1) Treatment of diazoxide improved the recovery of left ventricular developed pressure and decreased the leakage of myocardial enzymes, lactate dehydrogenase (LDH) and creatine kinase (CK), at the 2nd and 4th minute of reperfusion of rat heart after hypothermic preservation for 3 h. (2) After hypothermic preservation for 8 h, diazoxide improved the recovery of left ventricular developed pressure and decreased the leakage of myocardial enzymes (LDH, CK and glutamic oxalic transaminase) during reperfusion. Moreover, left ventricular end-diastolic pressure was significantly lower in diazoxide-treated hearts than that of hearts in Celsior solution. (3) Diazoxide significantly decreased the water content of myocardium and increased coronary flow of the hearts compared with those in control after hypothermic preservation for 8 h. (4) Impairment of myocardial ultrastructure after 8 h hypothermic preservation was alleviated in hearts treated with 30 mol/L diazoxide. (5) The cardiac effects of 30 mol/L diazoxide were attenuated by a mitoK(ATP) blocker 5-hydroxydecanoate (100 micromol/L). CONCLUSION: Diazoxide as a supplementation in cardioplegia solution could enhance myocardial protection during hypothermic heart preservation via opening of mitochondrial K(ATP) channel.
Animals↗
Cardioprotective effects of mitochondrial KATP channels activated at different time.
BACKGROUND: Recent studies in adult hearts have indicated that KATP channels in the inner mitochondrial membrane are responsible for the protection. And we investigated whether opening of mitochondrial KATP channels (mKATP) could provide myocardial protection for immature rabbits and determined its role in cardioprotection. METHODS: Thirty-four 3-4-week-old rabbits, weighing 300 - 350 g, were divided randomly into five groups: Group I (control group, n = 8); Group II [diazoxide preconditioning group; n = 8; the hearts were pretreated with 100 micromol/L diazoxide for 5 minutes followed by 10-minute wash out with Krebs-Henseleit buffer (KHB)]; Group III [diazoxide + 5-hydroxydeconate (5-HD) preconditioning group; n = 5; the hearts were pretreated with 100 micromol/L diazoxide and 100 micromol/L 5-HD); Group IV (diazoxide + cardioplegia group; n = 8; cardioplegia containing 100 micromol/L diazoxide perfused the hearts for 5 minutes before ischemia); Group V (diazoxide + 5-HD + cardioplegia group; n = 5; the cardioplegia contained 100 micromol/L diazoxide and 100 micro mol/L 5-HD). All hearts were excised and connected to langendrff perfusion system and passively perfused with KHB at 38 degrees C under a pressure of 70 cmH(2)O. After reperfusion, the recovery rate of left ventricular diastolic pressure (LVDP), +/-dp/dtmax, coronary flow (CF), the creatinine kinase (CK), lactate dehydrogenase (LDH), aspartate aminotransferase (AST) in coronary sinus venous effluent and the tissue ATP were measured. Mitochondria were evaluated semiquantitatively by morphology. RESULTS: After ischemia and reperfusion (I/R), the two groups that were treated by diazoxide only (Groups II and IV) had a significant improvement in LVDP, +/-dp/dtmax, and CF recovery. AST, LDH, and CK were decreased, and the levels of tissue ATP in the two groups were higher. Mitochondria was protected better in Group IV than in other groups. CONCLUSIONS: Activating mKATP channels before and during ischemia can similarly protect immature rabbit hearts, and the mechanism is related to the direct protective effect on mitochondria. Opening of mKATP channel during ischemia provides a better protection for mitochondria than it does before ischemia.
Adenosine Triphosphate↗
Effect of mitochondrial KATP channel on voltage-gated K+ channel in 24 hour-hypoxic human pulmonary artery smooth muscle cells.
BACKGROUND: Hypoxic pulmonary hypertension (HPH) is initiated by inhibition of O2-sensitive, voltage-gated (Kv) channels in pulmonary arterial smooth muscle cells (PASMCs). The mechanism of hypoxic pulmonary hypertension has not yet been fully elucidated. The mitochondrial ATP-sensitive K+ channel (MitoKATP) is extremely sensitive to hypoxia, and is a decisive factor in the control of mitochondrial membrane potential (DeltaPsim). This study investigated the changes of cell membrane potential and Kv channel in cultured human pulmonary artery smooth muscle cell (hPASMC) exposed to 24 hour-hypoxia, and explored the role of MitoKATP and DeltaPsim in this condition. METHODS: Fresh human lung tissues were obtained from the patients undergoing a chest operation. hPASMCs were isolated, cultured, and divided into 6 groups: (1) control group, cultured under normoxia; (2) diazoxide group, cultured in normoxia with diazoxide, an opener of MitoKATP; (3) 5-HD group, cultured in normoxia with sodium 5-hydroxydecanoate (5-HD), an antagonist of MitoKATP; (4) 24 hour-hypoxia group; (5) 24 hour-hypoxia + diazoxide group; and (6) 24 hour-hypoxia + 5HD group. Whole-cell patch-clamp technique was used to trace the cell membrane K+ currents. The expressions of cell membrane Kv1.5 mRNA and protein were determined by RT-PCR and Western blot technique, respectively. The relative changes in mitochondrial potential were tested with rhodamine fluorescence (R-123) technique. RESULTS: After exposure to diazoxide for 24 hours, the intensity of R-123 fluorescence in normoxic hPASMCs was significantly increased compared with control group (P < 0.05), but there were no significant changes in these tests after the hPASMCs had been exposed to 5-HD for 24 hours. Twenty-four hour-hypoxia or 24 hour-hypoxia + diazoxide could markedly increase the intensity of R-123 fluorescence in hPASMC and the changes were more significant in 24 hour-hypoxia +diazoxide group than in 24 hour-hypoxia group (P < 0.05) although 5-HD could partly weaken the effect of 24 hour-hypoxia on the intensity of R-123 fluorescence. After exposure to diazoxide for 24 hours, the cell membrane K+ currents and the expression of cell membrane Kv1.5 mRNA and protein in normoxic hPASMCs were significantly decreased compared with control group (P < 0.05), but there were no significant changes in these tests after the hPASMCs had been exposed to 5-HD for 24 hours. Also, 24 hour-hypoxia or 24 hour-hypoxia + diazoxide decreased the cell membrane K+ currents and the expression of Kv1.5 mRNA and protein (P < 0.05) but the changes were more significant in 24 hour-hypoxia + diazoxide group than in 24 hour-hypoxia group (P < 0.05). Again, 5-HD could partly weaken the inhibitory effect of 24 hour-hypoxia on the cell membrane K+ currents and the expression of Kv1.5 mRNA or protein (P < 0.05). CONCLUSIONS: The opening of MitoKATP followed by a depolarization of DeltaPsim in hypoxia might contribute to the alterations in the expression of cell membrane Kv1.5 mRNA and protein leading to change in the cell membrane potential of hypoxic hPASMCs. This might be a mechanism of the development of hypoxic pulmonary hypertension.
Cell Hypoxia↗
Mitochondrial K(ATP) channel as an end effector of cardioprotection during late preconditioning: triggering role of nitric oxide.
Nitric oxide (NO) has been implicated in the "second-window" of ischemic preconditioning (PC). However, the identity of the end effector after initiation of preconditioning by NO is not known. It is likely that NO is involved in opening of mitochondrial ATP-sensitive potassium (mitoK(ATP)) channels. We hypothesized that NO is an important trigger for the opening of mitoK(ATP) channels in the late phase of preconditioning and inducible nitric oxide synthase (iNOS) up-regulation via NF kappa B plays a critical role in diazoxide-induced cardioprotection. To examine this, diazoxide (7 mg/kg) was administered to wild-type (WT) mice and mice lacking the gene 24 hours before 40 minutes of global ischemia. Hearts were perfused in a Langendorff mode and effects of activation of mitoK(ATP) channel and other interventions on functional, biochemical and pathological changes in ischemic hearts were assessed. In hearts from WT mice treated diazoxide, left-ventricular-developed pressure, end-diastolic pressure and coronary flow were significantly improved after ischemia/reperfusion (I/R); lactate dehydrogenase (LDH) release was also significantly decreased, while ATP contents were significantly higher. Administration of 5-HD, a specific blocker of mitoK(ATP) channel or l -NAME, an inhibitor of iNOS before I/R, during diazoxide-pretreatment completely blocked the late cardioprotection against ischemia. Late cardioprotection was also blocked by inhibition of either PKC- delta by rottlerin or NF kappa B by DDTC before diazoxide pretreatment. Diazoxide pretreatment significantly increased nuclear translocation of p65 which was blocked by protein kinase C (PKC) or nitric oxide synthase (NOS) inhibition. Diazoxide was totally inefffective in iNOS knockout mice. These results suggest that diazoxide activates NF kappa B via PKC signaling pathway and that leads to iNOS up-regulation after 24 hours. NO which is generated upon ischemic stress triggers the opening of mitoK(ATP)channel as an end effector of cardioprotection during late PC.
Acetophenones↗
Mitochondrial ATP-sensitive channel opener does not induce vascular preconditioning, but potentiates the effect of a preconditioning ischemia on coronary reactive hyperemia in the anesthetized goat.
Preconditioning ischemia (PI) increases the speed of the initial vasodilatation (vascular preconditioning) of a subsequent coronary reactive hyperemia (CRH) and reduces total hyperemic flow (THF). We investigated whether changes in CRH similar to those induced by PI are obtained with diazoxide, a mitochondrial ATP-sensitive K+ channel opener, and whether diazoxide influences the effects of a subsequent PI on CRH. In anesthetized goats, flow was recorded from the left circumflex coronary artery (LCCA). CRH and PI were obtained with 15-s and 5-min LCCA occlusions, respectively. CRH was studied before and after PI, before and after diazoxide (2.5 mg/kg i.v.) as well as before and after PI was induced after diazoxide pre-treatment. After PI, the time to peak (ttp) of CRH and THF decreased by 51+/-13% and 23+/-8%, respectively. Diazoxide did not change CRH. After diazoxide and PI, when basal flow had returned to the control level, the ttp of CRH was reduced as after PI alone (-45+/-12%), whereas THF was reduced to a greater extent (-41+/-9% versus -23+/-8%; P<0.01). In conclusion, PI alters CRH by decreasing THF and reducing the ttp of CRH. Whilst diazoxide does not reproduce the effects of PI on CRH, pre-treatment with diazoxide potentiates the effects of PI on THF.
Adenosine Triphosphate↗
Pharmacological preconditioning ameliorates neurological injury in a model of spinal cord ischemia.
BACKGROUND: Pharmacological openers of mitochondrial ATP-sensitive potassium (mitoKATP) channels have been shown to mimic ischemic preconditioning (IPC) in both the brain and myocardium. We hypothesized that similar endogenous mechanisms exist in the spinal cord and that diazoxide, a potent mitoKATP opener, could reduce neurologic injury after aortic cross-clamping in a model of spinal cord ischemia. METHODS: The infra-renal aorta was cross-clamped in 45 male New Zealand white rabbits for 20 minutes. Control animals received no pretreatment. Diazoxide-treated animals were dosed (5 mg/kg) 15 minutes before cross-clamp. A third group underwent 5 minutes of IPC 30 minutes before cross-clamp. Two groups received KATP antagonists, 5-hydroxydecanoic acid (5-HD, 20 mg/kg) or glibenclamide (1.0 mg/kg), before diazoxide administration. Systemic hypotension was induced in a final group with excess isoflurane. Tarlov Scoring was used to assess neurologic function at 24 and 48 hours, after which, the spinal cords were procured for histopathological analysis. RESULTS: Tarlov scoring demonstrated marked improvement in the Diazoxide group compared with control at 24 hours (p < 0.02) and 48 hours (p < 0.009). Moreover, no further neurologic injury occurred in this group at 7 days. IPC-treated animals showed neurologic improvement but were not significantly different from controls. Further, administration of glibenclamide was effective in antagonizing diazoxide's protective effect. CONCLUSIONS: Administration of diazoxide resulted in significant improvement in neurologic outcome in this model. This protective effect improved outcome at both early and late time points. Further, the antagonistic effect of glibenclamide implicates diazoxide's ATP-dependent potassium channel agonism as the mechanism of protection. Overall, this study suggests that diazoxide may be useful in the prevention of neurologic injury after thoracic aneurysm surgery.
Animals↗
ATP-gated K(+) channel openers enhance opioid antinociception: indirect evidence for the release of endogenous opioid peptides.
The ATP-gated K(+) channel openers - diazoxide, levcromakalim and morphine - enhance K(+) efflux by opening ATP-gated K(+) channels, thereby inducing cell hyperpolarization. Hyperpolarization decreases intracellular Ca(2+) levels, which leads to a decrease in neurotransmitter release contributing to the antinociceptive effects of the drugs. Previous findings implicate the release of endogenous opioids as the mediator of the antinociceptive effects of ATP-gated K(+) channel openers. Diazoxide and levcromakalim, administered intracerebroventricularly (i.c.v.), produced dose-dependent antinociception as determined by the tail-flick method ¿ED(50) 44 microg/mouse [95% confidence limits (CLs) from 28 to 68 microg/mouse] for diazoxide¿. Glyburide (10 microg/mouse), an ATP-gated K(+) channel antagonist, attenuated the effects of diazoxide, levcromakalim and morphine. Diazoxide- and levcromakalim-induced antinociception were both antagonized by CTOP (D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr amide), a mu-opioid receptor selective antagonist, and ICI 174,864 (N, N-diallyl-Tyr-Aib-Aib-Phe-Leu), a delta-opioid receptor antagonist, but were differentially attenuated by the kappa-opioid receptor antagonist, nor-Binaltorphimine. Combinations of inactive doses of the K(+) channel openers and opioid receptor agonists produced significant antinociceptive enhancement. Diazoxide (2 microg/mouse) shifted morphine's dose-response curve 47-fold, while levcromakalim (0.1 microg/mouse) shifted the curve 27-fold. The dose-response curve of kappa-opioid receptor agonist U50,488H (trans-(+/-)-3, 4 Dichloro-N-[2-(1-pyrrolidinyl)-cyclohexyl] benzeneacetamide methane sulfonate) was shifted 106-fold by diazoxide in a parallel manner, while levcromakalim administration increased the potency of U50,488H by 15-fold. Diazoxide shifted the dose-response curve of the delta-opioid receptor agonist, DPDPE [(D-Pen(2,5))-enkephalin], leftward in a non-parallel manner, while DPDPE was 6-fold more potent when combined with levcromakalim. We hypothesize that endogenous opioids mediate ATP-gated K(+) channel opener-induced antinociception and enhancement of opioids.
3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗
Critical timing of mitochondrial K(ATP) channel opening for enhancement of myocardial tolerance against infarction.
OBJECTIVE: The present study was designed to assess the relationship between the timing of a mitoK(ATP) channel opener, diazoxide, and its infarct size-limiting effect. METHODS: In isolated rabbit hearts, infarction was induced by 30 min of global ischemia and 2 h of reperfusion, and infarct size was determined by tetrazolium staining and expressed as a percentage of the left ventricle (%IS/LV). Diazoxide, a mitoK(ATP) channel selective opener, and/or 5-hydroxydecanoate (5-HD), a mitoK(ATP) channel blocker, were infused before or after the onset of ischemia. When these agents were infused during the ischemic period, they were dissolved in a hypoxic buffer at concentrations 10-fold higher than those in the pre-ischemic period, and the infusion rate was set at 2% of the pre-ischemic coronary flow. RESULTS: In untreated controls, %IS/LV was 53.2+/-4.1 (SE). Pretreatment with diazoxide (100 microM) with a 10-min washout period reduced %IS/LV to 7.8+/-2.4 and this protection was abolished by co-infusion of 5-HD (50 microM). Pre-ischemic infusion of diazoxide without a washout period reduced %IS/LV to 7.3+/-1.4, and infusion of diazoxide from 10 min after the onset of ischemia also limited %IS/LV to 14.9+/-4.6. However, diazoxide infusion from 25 min after the onset of ischemia failed to reduce infarct size (%IS/LV = 54.5+/-7.2). Furthermore, pretreatment with 5-HD (50 microM) also completely abolished the protection afforded by early post-ischemic diazoxide infusion (%IS/LV = 48.3+/-6.5). Neither infusion of 5-HD nor the anoxic vehicle alone during ischemia modified %IS/LV. CONCLUSION: These findings suggest that opening of mitoK(ATP) channels before ischemia and during early ischemia, but not that upon reperfusion, is important for enhancement of myocardial tolerance against infarction.
Animals↗
Both metabolic inhibition and mitochondrial K(ATP) channel opening are myoprotective and initiate a compensatory sarcolemmal outward membrane current.
BACKGROUND: Blockade of oxidative phosphorylation may activate ATP sensitive mitochondrial potassium (mitoK(ATP)) channels. We examined whether both metabolic inhibition and mitoK(ATP) channel openers protect both the whole organ and isolated cells from ischemia. METHODS AND RESULTS: Using a Langendorff preparation, one group of isolated rabbit hearts were exposed to ischemic preconditioning (IPC) via 2 episodes of flow interruption. The second group of hearts was preconditioned with 2 episodes of either the metabolic inhibitor, sodium cyanide (NaCN), or the mitoK(ATP) channel opener, diazoxide. The third group of hearts was exposed to the mitoK(ATP) channel inhibitor, 5-hydroxydecanoic acid (5-HD) prior to preconditioning with NaCN, diazoxide or IPC. Controls had no drug infused. Then, ischemia was induced in all hearts by left anterior descending coronary artery occlusion and infarct size was determined. Compared with controls (40+/-3%), infarct size was significantly reduced in hearts preconditioned with NaCN, diazoxide or IPC (18+/-3%, 26+/-3%, 21+/-2%, respectively; P<0.05 versus control). These reductions were reversed by 5-HD (36+/-3%, 33+/-2%, 37+/-2%; NaCN, diazoxide, IPC, respectively). Secondly, whole cell patch clamped isolated guinea pig ventricular myocytes were preconditioned with 2 episodes of either NaCN or diazoxide followed by Tyrodes perfusion with membrane potential set to -70 mV. Control cells were exposed to Tyrodes solution. All cells were then clamped to -20 mV and exposed to NaCN, which caused induction of an outward potassium current. Compared with controls, the average time to induction of the outward current was significantly reduced in cells preconditioned with either brief application of NaCN (11.6+/-1.8 versus 5.1+/-1.0 minutes, control versus NaCN, P<0.05) or diazoxide (5.5+/-1.4 versus 2.0+/-0.8 minutes, control versus diazoxide, P<0.05). CONCLUSIONS: Preconditioning protects the heart through mitoK(ATP). This protection also alters a surface membrane current, which may be important in myocardial protection.
Animals↗