Mitochondria are the main ATP source for a cytosolic pool controlling the activity of ATP-sensitive K+ channels in mouse cardiac myocytes

Objective: The aim was to identify the major ATP source controlling the activity of sarcolemmal K-ATP channels in ventricular cardiomyocytes. Methods: K-ATP-channel current (I-KATP) was measured with the patch-clamp technique in either the whole-cell (glycogenolysis blocked by 10 mmol/l (EGTA), cell-attached, or inside-out configuration. Results: In the absence of any substrate, (amplitude 31 +/-4 nA; n=5) appeared spontaneously 520+/-60 s (n=6) after whole-cell access. This latency was shortened by exposure to anoxia (117+/-33 s, n=32) and even more by uncoupling (1-10 mumol/l FCCP; 25+/-3 s: n=13) while the amplitude was unchanged, During metabolic inhibition the latency was remarkably prolonged when the F1F0-ATPase was blocked by oligomycin, suggesting that under those conditions the F1F0-ATPase is the major ATP consumer. Glucose (15.5-20.0 mmol/l) in the bath solution did not affect the amplitude of I-KATP but prolonged its latency compared to respective substrate-free conditions. However, I-KATP was blocked immediately by mitochondrial substrates. FCCP also induced large in cell-attached measurement,, in either the absence or presence of glucuse and oligomycin. Conclusions: The activity of K-ATP channels in cardiomyocytes of mice is controlled by a cytosolic [ATP] pool for which oxidative phosphorylation is the predominant ATP source. (C) 2001 Elsevier Science B.V. All rights reserved.