Slack K+ channels confer protection against myocardial ischaemia/reperfusion injury

Na+-activated Slack potassium (K+) channels are increasingly recognized as regulators of neuronal activity, yet little is known about their role in the cardiovascular system. Slack activity increases when intracellular Na+ concentration ([Na+]i) reaches pathophysiological levels. Elevated [Na+]i is a major determinant of the ischaemia and reperfusion (I/R)-induced myocardial injury; thus, we hypothesized that Slack plays a role under these conditions.

K+ currents in cardiomyocytes (CMs) obtained from wildtype but not from global Slack knockout mice were sensitive to electrical inactivation of voltage-sensitive Na+ channels. Live-cell imaging demonstrated that K+ fluxes across the sarcolemma rely on Slack, while the depolarized resting membrane potential in Slack-deficient CMs led to excessive cytosolic Ca2+ accumulation and finally to hypoxia/reoxygenation-induced cell death. Cardiac damage in an in vivo model of I/R was exacerbated in global and CM-specific conditional Slack mutants and largely insensitive to mechanical conditioning manoeuvres. Finally, the protection conferred by mitochondrial ATP-sensitive K+ (mitoKATP) channels required functional Slack in CMs.

Collectively, our study provides evidence for Slack's crucial involvement in the ion homeostasis of no or low O2-stressed CMs. Thereby, Slack activity opposes the I/R-induced fatal Ca2+-uptake to CMs supporting the cardioprotective signaling attributed to mitoKATP function.