ATP consumption by uncoupled mitochondria activates sarcolemmal KATP channels in cardiac myocytes

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Abstract
We tested whether close coupling exists between mitochondria and sarcolemma by monitoring whole cell ATP-sensitive K+ (KATP) current ( I K,ATP) as an index of subsarcolemmal energy state during mitochondrial perturbation. In rabbit ventricular myocytes, either pinacidil or the mitochondrial uncoupler dinitrophenol (DNP), which rapidly switches mitochondria from net ATP synthesis to net ATP hydrolysis, had little immediate effect on I K,ATP. In contrast, in the presence of pinacidil, exposure to 100 μM DNP rapidly activated I K,ATP with complex kinetics consisting of a quick rise [time constant of I K,ATP increase (τ) = 0.13 ± 0.01 min], an early partial recovery (τ = 0.43 ± 0.04 min), and then a more gradual increase. This DNP-induced activation of I K,ATP was reversible and accompanied by mitochondrial flavoprotein oxidation. The F1F0-ATPase inhibitor oligomycin abolished the DNP-induced activation of I K,ATP. The initial rapid rise in I K,ATP was blunted by atractyloside (an adenine nucleotide translocator inhibitor), leaving only a slow increase (τ = 0.66 ± 0.17 min, P < 0.01). 2,4-Dinitrofluorobenzene (a creatine kinase inhibitor) slowed both the rapid rise (τ = 0.20 ± 0.01 min, P < 0.05) and the subsequent declining phase (τ = 0.88 ± 0.19 min, P < 0.05). From single KATP channel recordings, we excluded a direct effect of DNP on KATP channels. Taken together, these results indicate that rapid changes in F1F0-ATPase function dramatically alter subsarcolemmal energy charge, as reported by pinacidil-primed KATP channel activity, revealing cross-talk between mitochondria and sarcolemma. The effects of mitochondrial ATP hydrolysis on sarcolemmal KATP channels can be rationalized by reversal of F1F0-ATPase and the facilitation of coupling by the creatine kinase system.

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