Apoptosis repressor with caspase domain inhibits cardiomyocyte apoptosis by reducing K+ currents

Cell shrinkageis an early prerequisite in programmed cell death, and cytoplasmicK⁺ is a dominant cation that controls intracellular ionhomeostasis and cell volume. Blockade of K⁺ channelsinhibits apoptotic cell shrinkage and attenuates apoptosis. We examined whether apoptotic repressor with caspase recruitment domain (ARC), an antiapoptotic protein, inhibits cardiomyocyte apoptosis by reducing K⁺ efflux throughvoltage-gated K⁺ (Kv) channels. In heart-derived H9c2cells, whole cell Kv currents (I_K(V)) wereisolated by using Ca²⁺-free extracellular (bath) solutionand including 5 mM ATP and 10 mM EGTA in the intracellular (pipette)solution. Extracellular application of 5 mM 4-aminopyridine (4-AP), ablocker of Kv channels, reversibly reduced I_K(V)by 50-60% in H9c2 cells. The remaining currents during 4-APtreatment may be generated by K⁺ efflux through4-AP-insensitive K⁺ channels. Overexpression of ARC inheart-derived H9c2 cells significantly decreasedI_K(V), whereas treatment with staurosporine, apotent apoptosis inducer, enhanced I_K(V)in wild-type cells. The staurosporine-induced increase inI_K(V) was significantly suppressed and thestaurosporine-mediated apoptosis was markedly inhibited incells overexpressing ARC compared with cells transfected with thecontrol neomycin vector. These results suggest that theantiapoptotic effect of ARC is, in part, due to inhibition of Kvchannels in cardiomyocytes.