Calcium-sensing receptor activating phosphorylation of PKC[delta] translocation on mitochondria to induce cardiomyocyte apoptosis during ischemia/reperfusion

The calcium-sensing receptor (CaSR) is a G protein-coupled receptor (GPCR) that activates intracellular effectors; for example, it causes inositol phosphate (IP) and 1,2 diacylglycerol (DAG) accumulation, stimulating the release of intracellular calcium and the activation of the protein kinase Cs (PKCs). The activation of CaSR by ischemia/reperfusion (I/R) induces cardiomyocyte apoptosis through the mitochondrial apoptotic pathway; however, the underlying mechanisms remain unclear. In this study, rat hearts were subjected to 30 min of ischemia followed by 2 h of reperfusion in the presence of a CaSR activator, Gd[Cl.sub.3]. Our results revealed that, under these conditions, the expression of CaSR was increased, the number of apoptotic cardiomyocytes was significantly increased (as shown by terminal deoxy-nucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay) and the cells with a typical apoptotic morphology were observed using transmission electron microscopy. Our data further showed that mitochondria isolated from hearts that had undergone I/R combined with Gd[Cl.sub.3] exhibited a significant increase in the translocation of phosphorylated PKC[delta] to the mitochondria, an increase in cytochrome c (cyt c) release from the mitochondria and a marked decrease in mitochondrial potential. The administration of rottlerin, an inhibitor of PKC[delta], significantly reduced reperfusion-induced apoptosis, phospho-PKC[delta] translocation to the mitochondria and the release of cyt c from the mitochondria. Thus, the involvement of CaSR in cardiac apoptosis through the mitochondrial pathway during I/R with Gd[Cl.sub.3] is related to phospho-PKC[delta] translocation to the mitochondria. Keywords Calcium-sensing receptor * PKC[delta] * Ischemia/reperfusion * Hearts