Protein kinase C inhibitors enhance endothelin-1 and attenuate vasopressin and angiotensin II evoked [Ca2+]i elevation in the rat cardiomyocyte.

Primary cultures of neonatal rat cardiomyocytes were pretreated for 16 h with either nonselective (staurosporine, 100 nM) or selective (NPC15437, 20 microM) protein kinase C (PKC) inhibitors. These inhibitors did not affect the basal cytosolic free calcium, [Ca2+]i, level (106 +/- 12 nM) as determined by fura-2 fluorescence methodology. Both agents significantly enhanced the maximal [Ca2+]i responses to endothelin-1 (ET-1) and attenuated the peak [Ca2+]i responses to arginine vasopressin and angiotensin II. They did not alter the EC50 values of any of these agonists. Since depletion of [Ca2+]o led to only partial attenuation of the enhanced response to ET-1 in the treatment groups, it is likely that PKC inhibition results in an exaggerated intracellular mobilization of Ca2+ to ET-1. It is concluded that PKC modulates agonist(s)-evoked intracellular Ca2+ mobilization and that the nature of regulation is governed by the agonist.