Inhibition of BK Ca channels protects neonatal hearts against myocardial ischemia and reperfusion injury.

BK Ca channels are large-conductance calcium and voltage-activated potassium channels that are heterogeneously expressed in a wide array of cells. Activation of BK Ca channels present in mitochondria of adult ventricular cardiomyocytes is implicated in cardioprotection against ischemia-reperfusion (IR) injury. However, the BK Ca channel's activity has never been detected in the plasma membrane of adult ventricular cardiomyocytes. In this study, we report the presence of the BK Ca channel in the plasma membrane and mitochondria of neonatal murine and rodent cardiomyocytes, which protects the heart on inhibition but not activation. Furthermore, K + currents measured in neonatal cardiomyocyte (NCM) was sensitive to iberiotoxin (IbTx), suggesting the presence of BK Ca channels in the plasma membrane. Neonatal hearts subjected to IR when post-conditioned with NS1619 during reoxygenation increased the myocardial infarction whereas IbTx reduced the infarct size. In agreement, isolated NCM also presented increased apoptosis on treatment with NS1619 during hypoxia and reoxygenation, whereas IbTx reduced TUNEL-positive cells. In NCMs, activation of BK Ca channels increased the intracellular reactive oxygen species post HR injury. Electrophysiological characterization of NCMs indicated that NS1619 increased the beat period, field, and action potential duration, and decreased the conduction velocity and spike amplitude. In contrast, IbTx had no impact on the electrophysiological properties of NCMs. Taken together, our data established that inhibition of plasma membrane BK Ca channels in the NCM protects neonatal heart/cardiomyocytes from IR injury. Furthermore, the functional disparity observed towards the cardioprotective activity of BK Ca channels in adults compared to neonatal heart could be attributed to their differential localization.