Sarcolemmal KATP Channels Research Articles

Role and mechanism of mitochondrial kATP channels in hind-limb ischaemic preconditioning (IPC) of distant muscle flaps against ischaemia/reperfusion (I/R) injury

Abstract Introduction: We reported previously that 3 cycles of 10min occlusion in a hind-limb of the pig by tourniquet application protected multiple distant muscle flaps against I/R injury (infarction) when these muscles are subsequently subjected to 4h ischaemia/48h reperfusion (Am.J.Physiol.285:H1435). There is evidence that kATP channels are involved in remote IPC. Here we used specific pharmacologic probes with known effective dose to investigate the role and mechanism of sarcolemmal kATP (skATP) and mitochondrial kATP (mkATP) channels in hind-limb remote IPC against muscle flap infarction. Methods: Pigs with bilateral lat. dorsi muscle flaps underwent 10min infusion of: (i)saline, (ii)PEG, (iii)PEG with the mkATP channel opener BMS191095(2mg/kg), (iv)saline before remote IPC, (v)saline with the skATP channel blocker HMR1098(3mg/kg) and (vi)saline with the mkATP channel blocker 5-HD(5mg/kg) before remote IPC. All muscle flaps underwent 4h ischaemia/48h reperfusion. Muscle content of ATP and myeloperoxidase activity was studied at 4h ischaemia and 1.5h reperfusion respectively. Results: The muscle infarct size (IS) of remote IPC (24+/−2%) and BMS191095 treatment (20+/−3%) were similar but higher (p Conclusions: mkATP but not skATP channels mediate remote IPC against muscle flap infarction and the mechanism involves energy preservation during ischaemia and anti-neutrophil accumulation during reperfusion to mitigate I/R injury. This information is important for development of pharmacologic preconditioning against infarction.

Myocardial injury and its prevention in the perioperative setting

Myocardial injury and its prevention in the perioperative setting

Hypoxia-induced preconditioning in adult stimulated cardiomyocytes is mediated by the opening and trafficking of sarcolemmal KATP channels.

The opening of sarcolemmal and mitochondrial ATP-sensitive K(+) (KATP) channels in the heart is believed to mediate ischemic preconditioning, a phenomenon whereby brief periods of ischemia/reperfusion protect the heart against myocardial infarction. Here, we have applied digital epifluorescent microscopy, immunoprecipitation and Western blotting, perforated patch clamp electrophysiology, and immunofluorescence/laser confocal microscopy to examine the involvement of KATP channels in cardioprotection afforded by preconditioning. We have shown that adult, stimulated-to-beat, guinea-pig cardiomyocytes survived in sustained hypoxia for approximately 17 min. An episode of 5-min-long hypoxia/5-min-long reoxygenation before sustained hypoxia dramatically increased the duration of cellular survival. Experiments with different antagonists of KATP channels, applied at different times during the experimental protocol, suggested that the opening of sarcolemmal KATP channels at the beginning of sustained hypoxia mediate preconditioning. This conclusion was supported by perforated patch clamp experiments that revealed activation of sarcolemmal KATP channels by preconditioning. Immunoprecipitation and Western blotting as well as immunofluorescence and laser confocal microscopy showed that the preconditioning is associated with the increase in KATP channel proteins in sarcolemma. Inhibition of trafficking of KATP channel subunits prevented preconditioning without affecting sensitivity of cardiomyocytes to hypoxia in the absence of preconditioning. We conclude that the preconditioning is mediated by the activation and trafficking of sarcolemmal KATP channels.

1035-219 The L-type calcium and sarcolemmal KATP channels may contribute to pacing-induced cardioprotection

1035-219 The L-type calcium and sarcolemmal KATP channels may contribute to pacing-induced cardioprotection

Diazoxide causes early activation of cardiac sarcolemmal KATP channels during metabolic inhibition by an indirect mechanism.

We have used isolated myocytes to investigate the effects of diazoxide on sarcolemmal KATP channel (sarcoKATP) activity and action potential failure during metabolic inhibition, and the role of these channels in protection of functional recovery on reperfusion. Isolated adult rat ventricular myocytes were exposed to metabolic inhibition (NaCN and iodoacetate) and reperfusion. Functional recovery was assessed from the ability of cells to contract on electrical stimulation and to recover calcium homeostasis, measured with fura-2. Action potentials and KATP currents were measured using patch clamp. Pretreatment with diazoxide (100 microM, 5 min) increased the proportion of cells that recovered contractile function after MI and reperfusion from 16.8 +/- 2.4% to 65.0 +/- 2.2% (p<0.001) and the proportion of cells in which [Ca2+]i recovered to <250 nM. Pretreatment also accelerated action potential and contractile failure during MI. In cell-attached patches, MI activated sarcoKATP channels after 224 +/- 11 s, and diazoxide pretreatment decreased this to 145 +/- 24 s (p<0.01). However, diazoxide present in the patch pipette did not accelerate sarcoKATP channel activation. Intracellular Mg2+ rose earlier in diazoxide-pretreated cells. The sarcoKATP blocker HMR 1883 delayed action potential failure and reduced diazoxide protection. Diazoxide pretreatment increases recovery of function and [Ca2+]i following reperfusion. Protection is coupled with early action potential failure, due to early activation of sarcoKATP channels during metabolic inhibition (MI), which is likely to involve an indirect effect of diazoxide.

Molecular mechanisms of the inhibitory effects of propofol and thiamylal on sarcolemmal adenosine triphosphate-sensitive potassium channels.

Both propofol and thiamylal inhibit adenosine triphosphate-sensitive potassium (KATP) channels. In the current study, the authors investigated the effects of these anesthetics on the activity of recombinant sarcolemmal KATP channels encoded by inwardly rectifying potassium channel (Kir6.1 or Kir6.2) genes and sulfonylurea receptor (SUR1, SUR2A, or SUR2B) genes. The authors used inside-out patch clamp configurations to investigate the effects of propofol and thiamylal on the activity of recombinant KATP channels using COS-7 cells transfected with various types of KATP channel subunits. Propofol inhibited the activities of the SUR1/Kir6.2 (EC50 = 77 microm), SUR2A/Kir6.2 (EC50 = 72 microm), and SUR2B/Kir6.2 (EC50 = 71 microm) channels but had no significant effects on the SUR2B/Kir6.1 channels. Propofol inhibited the truncated isoform of Kir6.2 (Kir6.2DeltaC36) channels (EC50 = 78 microm) that can form functional KATP channels in the absence of SUR molecules. Furthermore, the authors identified two distinct mutations R31E (arginine residue at position 31 to glutamic acid) and K185Q (lysine residue at position 185 to glutamine) of the Kir6.2DeltaC36 channel that significantly reduce the inhibition of propofol. In contrast, thiamylal inhibited the SUR1/Kir6.2 (EC50 = 541 microm), SUR2A/Kir6.2 (EC50 = 248 microm), SUR2B/Kir6.2 (EC50 = 183 microm), SUR2B/Kir6.1 (EC50 = 170 microm), and Kir6.2DeltaC36 channels (EC50 = 719 microm). None of the mutants significantly affects the sensitivity of thiamylal. These results suggest that the major effects of both propofol and thiamylal on KATP channel activity are mediated via the Kir6.2 subunit. Site-directed mutagenesis study suggests that propofol and thiamylal may influence Kir6.2 activity by different molecular mechanisms; in thiamylal, the SUR subunit seems to modulate anesthetic sensitivity.

Minoxidil: mechanisms of action on hair growth.

We have known for over 30 years that minoxidil stimulates hair growth, yet our understanding of its mechanism of action on the hair follicle is very limited. In animal studies, topical minoxidil shortens telogen, causing premature entry of resting hair follicles into anagen, and it probably has a similar action in humans. Minoxidil may also cause prolongation of anagen and increases hair follicle size. Orally administered minoxidil lowers blood pressure by relaxing vascular smooth muscle through the action of its sulphated metabolite, minoxidil sulphate, as an opener of sarcolemmal KATP channels. There is some evidence that the stimulatory effect of minoxidil on hair growth is also due to the opening of potassium channels by minoxidil sulphate, but this idea has been difficult to prove and to date there has been no clear demonstration that KATP channels are expressed in the hair follicle. A number of in vitro effects of minoxidil have been described in monocultures of various skin and hair follicle cell types including stimulation of cell proliferation, inhibition of collagen synthesis, and stimulation of vascular endothelial growth factor and prostaglandin synthesis. Some or all of these effects may be relevant to hair growth, but the application of results obtained in cell culture studies to the complex biology of the hair follicle is uncertain. In this article we review the current state of knowledge on the mode of action of minoxidil on hair growth and indicate lines of future research.

Risk of ventricular proarrhythmia with selective opening of the myocardial sarcolemmal versus mitochondrial ATP-gated potassium channel.

Myocardial ATP-gated potassium channels (K-ATPs) are critical in the intracellular signaling cascade resulting in ischemic preconditioning (IP). Mitochondrial K-ATP channels seem to be responsible for IP, whereas the functions of K-ATP channels in the sarcolemmal membrane are less well understood. The proarrhythmic potential of specific versus nonspecific opening of K-ATP channels has not been investigated. In this study, Langendorff-perfused rabbit hearts were exposed to either pinacidil (1.25 microM), a nonselective K-ATP channel agonist, or selective mitochondrial or sarcolemmal K-ATP channel agonists or antagonists. The hearts were then subjected to 12 min of hypoxic perfusion and 40 min of reoxygenation. Hearts were monitored for the induction of ventricular fibrillation (VF). No heart subjected to hypoxia-reoxygenation without drug treatment developed VF (0 of 5). Pinacidil pretreatment induced VF (12 of 14; p = 0.004 versus control). Pinacidil's effect was blocked by HMR-1098 (1-[5-[2-(5-chloro-o-anisamide)ethyl]-2-methoxyphenyl]sulfonyl]-3-methylthiourea) (1 microM), a selective sarcolemmal K-ATP channel antagonist (1 of 7; p = 0.007 versus pinacidil; N.S. versus control). Hearts pretreated with 5-hydroxydecanoate (5-HD) (100 microM), a putatively selective mitochondrial K-ATP channel blocker developed VF in one of eight trials (N.S. versus control). 5-HD did not alter the effects of pinacidil (6 of 8; p < 0.05 versus control; N.S. versus pinacidil alone). Selective mitochondrial K-ATP channel activation with [(3R)-trans-4-((4-chlorophenyl)-N-(1H-imidazol-2-ylmethyl)dimethyl-2H-1-benzopyran-6-carbonitril monohydrochloride] (BMS-191095) (6 microM) resulted in zero of five hearts developing VF (N.S. versus control). Our data suggest that selective opening of the sarcolemmal K-ATP channel during hypoxia-reoxygenation induced VF, whereas opening of the mitochondrial channel was not associated with VF. The findings suggest that caution should be exercised when developing compounds aimed at inducing IP, and nonspecific opening of the K-ATP channel should be avoided.

Effect of the cardioselective, sarcolemmal K(ATP) channel blocker HMR 1098 on atrial electrical remodeling during pacing-induced atrial fibrillation in dogs.

The progressive shortening of the atrial effective refractory period (ERP) during atrial fibrillation (AF) might be due to the activation of the KATP channels by rapid atrial rates. We tested the hypothesis that the cardioselective, sarcolemmal KATP channel blocker HMR 1098 would prevent atrial ERP shortening during AF. Nine dogs were treated with HMR 1098 (3 mg/kg bolus injection followed by a continuous intravenous (i.v.) infusion at 17 microg/kg/min rate maintained throughout the study) and 7 dogs served as controls receiving i.v. saline. Pharmacological autonomic blockade was induced by i.v. administration of atropine (0.04 mg/kg) and propranolol (0.2 mg/kg) and maintained throughout the study by continuous i.v. infusion of atropine (0.007 mg/kg/h) and propranolol (0.04 mg/kg/h). Rapid right atrial pacing at 50 msec cycle length (CL) was initiated and maintained for 6 hours. High right atrial ERP (HRA-ERP) and corrected sinus node recovery time (HRA-cSNRT), coronary sinus ERP (CS-ERP) and corrected SNRT (CS-cSNRT) at three (400, 300, 200 msec) CLs were measured before and after pacing at different time points. Baseline values were not different between control and treated dogs. In the control group the HRA-ERP progressively shortened (from 179 +/- 21 msec at baseline to 161 +/- 23 msec at 360 min at 400 msec CL) ( p = 0.002), with a gradual decrease, loss or inversion of ERP rate adaptation at shorter (300, 200 msec) CLs. HMR 1098 treatment did not prevent the shortening of HRA-ERP during the first 2 to 3 hours of rapid atrial pacing. However, beginning at 180-240 min, HMR 1098 increased the HRA-ERP ( p = 0.01) to baseline by 360 min. HMR 1098 treatment did not prevent another feature of atrial electrical remodeling, the flattening or inversion of ERP rate adaptation. In neither group did CS-ERP shortening occur. The maximum cSNRT at 360 min prolonged significantly in both groups during HRA and CS pacing as well compared with baseline. HMR 1098 treatment did not prevent the shortening of HRA-ERP, the salient feature of atrial electrical remodeling in the first 2 to 3 hours of rapid atrial rates, but did prevent it thereafter. Another characteristic feature of atrial electrical remodeling, the flattening or inversion of physiological ERP rate adaptation was not prevented by HMR 1098 treatment. Sinus node depression was detectable after short-term (6 hours) rapid atrial pacing and was not affected by HMR 1098.

Roles of KATP channels in delayed cardioprotection and intracellular Ca(2+) in the rat heart as revealed by kappa-opioid receptor stimulation with U50488H.

The effect of preconditioning with U50488 H (UP), a selective kappa-opioid receptor (kappa-OR) agonist, on infarct size and intracellular Ca2+ ([Ca2+]i) in the heart subjected to ischaemic insults were studied and evaluated. U50488 H administered intravenously reduced the infarct size 18-48 h after administration in isolated hearts subjected to regional ischaemia/reperfusion (I/R). The effect was dose dependent. A peak effect was reached at 10 mg x kg-1 U50488 H and at 24 h after administration. The effect of 10 mg x kg-1 U50488 H at 24 h after administration was abolished by nor-binaltorphimine (nor-BNI), a selective kappa-OR antagonist, indicating the effect was kappa-OR mediated. The infarct reducing effect of U50488 H was attenuated when a selective blocker of mitochondrial (5-hydroxydecanoic acid, 5-HD) or sarcolemmal (HRM-1098) ATP-sensitive potassium channel (KATP) was coadministered with U50488 H 24 h before ischaemia or when 5-HD was administered just before ischaemia. U50488 H also attenuated the elevation in [Ca2+]i and reduction in electrically induced [Ca2+]i transient in cardiomyocytes subjected to ischaemic insults. The effects were reversed by blockade of KATP channel, which abolished the protective effect of preconditioning with U50488 H. The results indicated that mitochondrial KATP channel serves as both a trigger and a mediator, while sarcolemmal KATP channel as a trigger only, of delayed cardioprotection of kappa-OR stimulation. The effects of these channels may result from prevention/attenuation of [Ca2+]i overload induced by ischaemic insults.

KATP channels and myocardial preconditioning: an update.

Ischemic or myocardial preconditioning (IPC) is a phenomenon whereby brief periods of ischemia have been shown to protect the myocardium against a more sustained ischemic insult. The result of IPC may be manifest as a marked reduction in infarct size, myocardial stunning, or incidence of cardiac arrhythmias. Whereas many endogenous neurotransmitters, peptides, and hormones have been proposed to play a role in the signal transduction pathways mediating the cardioprotective effect of IPC, nearly universal evidence indicates the involvement of the ATP-sensitive potassium (KATP) channel. Initial evidence suggested that the surface or sarcolemmal KATP (sarcKATP) channel triggered or mediated the cardioprotective effects of IPC; however, more recent findings have suggested a major role for a mitochondrial site or possibly a mitochondrial KATP channel (mitoKATP). This review presents evidence that supports a role for these two channels as a trigger and/or downstream mediator in the phenomenon of IPC or pharmacologically induced PC as well as recent evidence that suggests the involvement of a mitochondrial calcium-activated potassium (mitoKca) channel or the electron transport chain in mediating the beneficial effects of IPC or pharmacologically induced PC.

Journal-related Activities at the 2003 American Society of Anesthesiologists Annual Meeting

Journal-related Activities at the 2003 American Society of Anesthesiologists Annual Meeting

Na(+) current through KATP channels: consequences for Na(+) and K(+) fluxes during early myocardial ischemia.

During early myocardial ischemia, the myocytes are loaded with Na(+), which in turn leads to Ca(2+) overload and cell death. The pathway of the Na(+) influx has not been fully elucidated. The aim of the study was to quantify the Na(+) inward current through sarcolemmal KATP channels (IKATP,Na) in anoxic isolated cardiomyocytes at the actual reversal potential (Vrev) and to estimate the contribution of this current to the Na(+) influx in the ischemic myocardium. IKATP,Na was determined in excised single channel patches of mouse ventricular myocytes and macropatches of Xenopus laevis oocytes expressing SUR2A/Kir6.2 channels. In the presence of K+ ions, the respective permeability ratios for Na(+) to K(+) ions, PNa/PK, were close to 0.01. Only in the presence of Na(+) ions on both sides of the membrane was IKATP,Na similarly large to that calculated from the permeability ratio PNa/PK, indicative of a Na(+) influx that is largely independent of the K+ efflux at Vrev. With the use of a peak KATP channel conductance in anoxic cardiomyocytes of 410 nS, model simulations for a myocyte within the ischemic myocardium showed that the amplitude of the Na(+) influx and K(+) efflux is even larger than the respective fluxes by the Na(+) - K(+) pump and all other background fluxes. These results suggest that during early ischemia the Na(+) influx through KATP channels essentially contributes to the total Na+ influx and that it also balances the K(+) efflux through KATP channels.

Diazoxide triggers cardioprotection against apoptosis induced by oxidative stress.

Although mitochondrial ATP-sensitive potassium (mitoK(ATP)) channels have been reported to reduce the extent of apoptosis, the critical timing of mitoK(ATP) channel opening required to protect myocytes against apoptosis remains unclear. In the present study, we examined whether the mitoK(ATP) channel serves as a trigger of cardioprotection against apoptosis induced by oxidative stress. Apoptosis of cultured neonatal rat cardiomyocytes was determined by flow cytometry (light scatter and propidium iodide/annexin V-FITC fluorescence) and by nuclear staining with Hoechst 33342. Mitochondrial membrane potential (DeltaPsi) was measured by flow cytometry of cells stained with rhodamine-123 (Rh-123). Exposure to H(2)O(2) (500 microM) induced apoptosis, and the percentage of apoptotic cells increased progressively and peaked at 2 h. This H(2)O(2)-induced apoptosis was associated with the loss of DeltaPsi, and the time course of decrease in Rh-123 fluorescence paralleled that of apoptosis. Pretreatment of cardiomyocytes with diazoxide (100 microM), a putative mitoK(ATP) channel opener, for 30 min before exposure to H(2)O(2) elicited transient and mild depolarization of DeltaPsi and consequently suppressed both apoptosis and DeltaPsi loss after 2-h exposure to H(2)O(2). These protective effects of diazoxide were abrogated by the mitoK(ATP) channel blocker 5-hydroxydecanoate (500 microM) but not by the sarcolemmal K(ATP) channel blocker HMR-1098 (30 microM). Our results suggest for the first time that diazoxide-induced opening of mitoK(ATP) channels triggers cardioprotection against apoptosis induced by oxidative stress in rat cardiomyocytes.

Isoflurane decreases ATP sensitivity of guinea pig cardiac sarcolemmal KATP channel at reduced intracellular pH.

Volatile anesthetics can protect the myocardium against ischemic injury by opening the adenosine triphosphate (ATP)-sensitive potassium (K(atp)) channels. However, direct evidence for anesthetic-channel interaction is still limited, and little is known about the role K(atp) channel modulators play in this effect. Because pH is one of the regulators of K(atp) channels, the authors tested the hypothesis that intracellular pH (pHi) modulates the direct interaction of isoflurane with the cardiac K(atp) channel. The effects of isoflurane on sarcolemmal K(atp) channels were investigated at pHi 7.4 and pHi 6.8 in excised inside-out membrane patches from ventricular myocytes of guinea pig hearts. At pHi 7.4, intracellular ATP (1-1,000 microm) inhibited K(atp) channels and decreased channel open probability (Po) in a concentration-dependent manner with an IC(50) of 8 +/- 1.5 microm, and isoflurane (0.5 mm) either had no effect or decreased channel activity. Lowering pHi from 7.4 to 6.8 enhanced channel opening by increasing Po and reduced channel sensitivity to ATP, with IC shifting from 8 +/- 1.2 to 45 +/- 5.6 microm. When applied to the channels activated at pHi 6.8, isoflurane (0.5 mm) increased Po and further reduced ATP sensitivity, shifting IC(50) to 110 +/- 10.0 microm. Changes in pHi appear to modulate isoflurane interaction with the cardiac K(atp) channel. At pHi 6.8, which itself facilitates channel opening, isoflurane enhances channel activity by increasing Po and reduces sensitivity to inhibition by ATP without changing the unitary amplitude of single channel current or the conductance. These results support the hypothesis of direct isoflurane-K(atp) channel interaction that may play a role in cardioprotection by volatile anesthetics.

B-type natriuretic peptide limits infarct size in rat isolated hearts via KATP channel opening.

B-type natriuretic peptide (BNP) has been reported to be released from the myocardium during ischemia. We hypothesized that BNP mediates cardioprotection during ischemia-reperfusion and examined whether exogenous BNP limits myocardial infarction and the potential role of ATP-sensitive potassium (K(ATP)) channel opening. Langendorff-perfused rat hearts underwent 35 min of left coronary artery occlusion and 120 min of reperfusion. The control infarct-to-risk ratio was 44.8 +/- 4.4% (means +/- SE). BNP perfused 10 min before ischemia limited infarct size in a concentration-dependent manner, with maximal protection observed at 10(-8) M (infarct-to-risk ratio: 20.1 +/- 5.2%, P < 0.01 vs. control), associated with a 2.5-fold elevation of myocardial cGMP above the control value. To examine the role of K(ATP) channel opening, glibenclamide (10(-6) M), 5-hydroxydecanoate (5-HD; 10(-4) M), or HMR-1098 (10(-5) M) was coperfused with BNP (10(-8) M). Protection afforded by BNP was abolished by glibenclamide or 5-HD but not by HMR-1098, suggesting the involvement of putative mitochondrial but not sarcolemmal K(ATP) channel opening. We conclude that natriuretic peptide/cGMP/K(ATP) channel signaling may constitute an important injury-limiting mechanism in myocardium.

Infarct size limitation by nicorandil: Roles of mitochondrial KATP channels, sarcolemmal KATP channels, and protein kinase C

ObjectivesThis study aimed to examine: 1) whether nicorandil protects the ischemic myocardium by activating sarcolemmal adenosine triphosphate (ATP)-sensitive K+ (sarcKATP) channels or the mitochondrial KATP (mitoKATP) channels, and 2) whether protein kinase C (PKC) activity is necessary for cardioprotection afforded by nicorandil. BackgroundNicorandil is a hybrid of nitrate and a KATP channel opener that activates the sarcKATP and mitoKATP channels. Both of these KATP channels are regulated by PKC, and this kinase may be activated by nitric oxide and also by oxygen free radicals (OFR) generated after mitoKATP channel opening. MethodsIn isolated rabbit hearts, infarction was induced by 30-min global ischemia/2-h reperfusion with monitoring of the activation recovery interval (ARI), an index of action potential duration. Protein kinase C translocation was assessed by Western blotting. ResultsNicorandil did not change ARI before ischemia, but it accelerated ARI shortening after the onset of ischemia and reduced infarct size by 90%. A sarcKATP channel selective blocker, HMR1098, abolished acceleration of ischemia-induced ARI-shortening by nicorandil and eliminated 40% of nicorandil-induced infarct size limitation. A mitoKATP channel selective blocker, 5-hydroxydecanoate, abolished the protection afforded by nicorandil without affecting ARI. Cardioprotection by nicorandil was inhibited neither by an OFR scavenger, N-2-mercaptopropionylglycine nor by a PKC inhibitor, calphostin C, at a dose that was capable of inhibiting PKC-ε translocation after preconditioning. ConclusionsBoth the sarcKATP and mitoKATP channels are involved in anti-infarct tolerance afforded by nicorandil, but PKC activation induced by nitric oxide or OFR generation, if any, does not play a crucial role.

03 Action potential duration in diabetic and normal sheep hearts: Role of sarcolemmal KATP channel, insulin and hyperglycemia

03 Action potential duration in diabetic and normal sheep hearts: Role of sarcolemmal KATP channel, insulin and hyperglycemia

Ischemic preconditioning: a plea for rationally targeted clinical trials.

Time for primary review 20 days. The concept of myocardial ischemic ‘preconditioning’ (PC) has been with us since 1986 [1]. A tremendous body of research over the last 15 years has documented this phenomenon in virtually every species tested, with both an early and late phase of PC-induced cardioprotection, manifest ∼5–30 min and 12–24 h after the PC trigger, having been identified. A host of additional studies have yielded insight into the cellular mediators and complex second messenger pathways that purportedly contribute to the protection achieved with brief antecedent PC ischemia, with the currently favored paradigm involving initial stimulation of one or more G protein-coupled receptors; subsequent activation of multiple ‘in parallel’ or ‘in series’ kinases (i.e. including, among others, the e-isoform of protein kinase C and one or more isoforms of p38 mitogen activated protein kinase); followed by phosphorylation and activation of a membrane-bound end-effector, possibly the sarcolemmal and/or mitochondrial KATP channel. These mechanistic studies have, as an ancillary benefit, provided a rational framework for the identification of pharmacologic agents that, when given in lieu of brief ischemia, may effectively mimic the benefits of conventional ischemic PC. Perhaps most importantly, a substantial amount of evidence favors the concept that ischemic preconditioning (both early and delayed) can occur in human hearts. However, the translation of ischemic preconditioning from the experimental laboratory to clinical utility has been disappointing and slow. Our goals in this manuscript are to: (i) review the clinical models and scenarios in which conventional ischemic PC and/or pharmacologic PC-mimetic agents have shown promise in eliciting cardioprotection; (ii) summarize, for each of these multiple scenarios, the potential benefits that might be achieved in the implementation of PC as a therapeutic strategy; (iii) outline, for each of the relevant clinical settings, a proposed design for the multicenter trials … * Corresponding author. Tel.: +1-213-977-4050; fax: +1-213-977-4107 rkloner{at}goodsam.org

Contractility and ischemic response of hearts from transgenic mice with altered sarcolemmal K(ATP) channels.

The functional significance of ATP-sensitive K(+) (K(ATP)) channels is controversial. In the present study, transgenic mice expressing a mutant Kir6.2, with reduced ATP sensitivity, were used to examine the role of sarcolemmal K(ATP) in normal cardiac function and after an ischemic or metabolic challenge. We found left ventricular developed pressure (LVDP) was 15-20% higher in hearts from transgenics in the absence of cardiac hypertrophy. beta-Adrenergic stimulation caused a positive inotropic response from nontransgenic hearts that was not observed in transgenic hearts. Decreasing extracellular Ca(2+) decreased LVDP in hearts from nontransgenics but not in those from transgenics. These data suggest an increase in intracellular [Ca(2+)] in transgenic hearts. Additional studies have demonstrated hearts from nontransgenics and transgenics have a similar postischemic LVDP. However, ischemic preconditioning does not improve postischemic recovery in transgenics. Transgenic hearts also demonstrate a poor recovery after metabolic inhibition. These data are consistent with the hypothesis that sarcolemmal K(ATP) channels are required for development of normal myocardial function, and perturbations of K(ATP) channels lead to hearts that respond poorly to ischemic or metabolic challenges.