SUR2A C‐terminal fragments reduce K_ATP currents and ischaemic tolerance of rat cardiac myocytes

Abstract

C-terminal fragments of the sulphonylurea receptor SUR2A can alter the functional expression of cloned ATP-sensitive K + channels (K ATP ). To investigate the protective role of K ATP channels during metabolic stress we transfected SUR2A fragments into adult rat cardiac myocytes. A fragment comprising residues 1294-1358, the A-fragment, reduced sarcolemmal K ATP currents by over 85% after 2 days (pinacidil-activated current densities were: vector alone 7.04 ± 1.22; and A-fragment 0.94 ± 0.07 pA pF −1 , n = 6,6, P < 0.001). An inactive fragment (1358-1545, current density 6.30 ± 0.85 pA pF −1 , n = 6 ) was used as a control. During metabolic inhibition (CN and iodoacetate) of isolated myocytes stimulated at 1 Hz, the A-fragment delayed action potential shortening and contractile failure, but accelerated rigor contraction and increased Ca 2+ loading. On reperfusion, A-fragment-transfected cells also showed increased intracellular Ca 2+ and the proportion of cells recovering contractile function was reduced from 40.0 to 9.5% (P < 0.01). The protective effect of pretreatment with 2,4-dinitrophenol, measured from increased functional recovery and reduced Ca 2+ loading, was abolished by the A-fragment. Our data are consistent with a role for K ATP channels in causing action potential failure and reduced Ca 2+ loading during metabolic stress, and with a major role in protection by preconditioning. The effects of the A-fragment may arise entirely from reduced expression of the sarcolemmal K ATP channel, but we also discuss the possibility of mitochondrial effects.

Interaction of Cardiovascular Risk Factors with Myocardial Ischemia/Reperfusion Injury, Preconditioning, and Postconditioning

“…It has been proposed that a PKC-induced increased trafficking of K ATP to the sarcolemma (Budas et al, 2004), which opens sarcolemmal K ATP causing shortening of myocyte action potential duration and reduced Ca 2ϩ influx (Rainbow et al, 2004), is responsible for preconditioninginduced protection (Gross, 1995). However, a number of observations are inconsistent with this conjecture, including the demonstration of protection independent of surface current changes in isolated nonbeating myocytes (Garlid et al, 1997;Liu et al, 1998b) and the ability of some K ATP openers to protect against ischemia/ reperfusion injury at doses or concentrations that do not influence the action potential duration (Yao and Gross, 1994;Grover et al, 1995Grover et al, , 1996.…”

Early opening of sarcolemmal ATP-sensitive potassium channels is not a key step in PKC-mediated cardioprotection

“…Action potential and cell-attached patch recordings were made as previously described [19]. displaying a cardioprotected phenotype may be prepared using a "stop-start" perfusion protocol in a whole heart mounted on a Langendorff perfusion system prior to enzymatic isolation of cardiomyocytes [27].…”

“…Evidence for a key role for the cardiac K ATP channel comes from the observation that pharmacological blockade [12,18], disruption of channel expression with interacting fragments of SUR [19], shRNA knockdown [3] and knockout of Kir6.2 subunits [20,21] all have deleterious effects on the ability of IPC and other cardioprotective stimuli to impart protection.…”

Anesthetics and cardioprotection

“…However, some of the recent studies that involved the use of sarcK ATPspecific inhibitors and genetic models of disrupted or knocked-out sarcK ATP channel subunits indicated that the role of sarcK ATP channel in cardioprotection should not be ignored. (51,52) We have demonstrated that isoflurane can stimulate K ATP channels in isolated ventricular myocytes. (20,40,41,48,49,53,54) In addition, our laboratory has shown that the K ATP channel agonist pinacidil exerts greater effects to open the K ATP channel in myocytes that were previously subjected to isoflurane.…”