Activation of PKC-Alpha Increases Ca2+ Sparklet Activity in Cardiac Myocytes

Abstract

Ca2+ sparklets are local elevations in intracellular Ca2+ produced by the opening of a single or a small cluster of sarcolemmal L-type Cav1.2 Ca2+ channels. At present, however, the spatial organization and mechanisms of modulation of Ca2+ sparklets in cardiac myocytes is unknown. Here, we tested the hypothesis that Ca2+ sparklets activity varies within the sarcolemma of neonatal cardiac myocytes and that chemically-induced translocation of PKCα increases the Ca2+ sparklet activity in these cells. Consistent with this hypothesis we found that application of the PKC activator phorbol 12,13-dibutyrate (PDBu; 500 nM) increased Ca2+ sparklet activity in neonatal cardiac myocytes. Analysis of the spatial distribution Ca2+ sparklet activity was not random (i.e. did not have a Poisson distribution). Rather, as in reported in smooth muscle cells, Ca2+ sparklet activity was higher at specific regions of the cell. Translocation of PKCα to the sarcolemma of neonatal cardiac myocytes resulted in an increase in Ca2+ sparklet activity in specific regions of the cell. Data will be presented on the relationship between Ca2+ sparklet activity and Ca2+ release from the sarcoplasmic reticulum via ryanodine receptors (i.e. Ca2+ sparks) during excitation-contraction coupling. Our data suggest that Ca2+ sparklet (i.e. L-type Ca2+ channels) activity varies within the sarcolemma of neonatal cardiac myocytes and that they are modulated by PKCα, potentially regulating SR Ca2+ release during EC coupling in heart.