Cardiac metabolic effects of KNa1.2 channel deletion, and evidence for its mitochondrial localization

Controversy surrounds the molecular identity of mitochondrial K + channels that are important for protection against cardiac ischemia-reperfusion injury. While K Na 1.2 ( Kcnt2 gene) is necessary for cardioprotection by volatile anesthetics, electrophysiologic evidence for a channel of this type in mitochondria is lacking. The endogenous physiologic role of a potential mito-K Na 1.2 channel is also unclear. Herein, single channel patch-clamp of 27 independent cardiac mitochondrial inner membrane (mitoplast) preparations from wild type (WT) mice yielded 6 channels matching the known ion-sensitivity, ion-selectivity, pharmacology and conductance properties of K Na 1.2 (slope conductance 138±1 pS). However, similar experiments on 40 preparations from Kcnt2 -/- mice yielded zero such channels. The K Na opener bithionol uncoupled respiration in WT but not Kcnt2 -/- cardiomyocytes. Furthermore, when oxidizing only fat as substrate, Kcnt2 -/- cardiomyocytes and hearts were less responsive to increases in energetic demand. Kcnt2 -/- mice also had elevated body fat, but no baseline differences in the cardiac metabolome. These data support the existence of a cardiac mitochondrial K Na 1.2 channel, and a role for cardiac K Na 1.2 in regulating metabolism under conditions of high energetic demand.