Effect of modulators of protein kinase C activity on Ca2+ transport in retinal rod microsomes.

The effect of modulators of protein kinase C (PKC) activity on Ca2+ translocation in retinal rod microsomes was studied. It is shown that PKC activators (phorbol 12-myristate-13-acetate (PMA) and diacylglycerol (DAG)) and inhibitors (chelerythrine chloride, polymyxin B, and phloretin) stimulate and inhibit ATP-dependent Ca2+ uptake in retinal rod microsomes, respectively. This effect is apparently due to an influence of PKC on Ca-ATPase contained in these vesicular structures. It was found that PKC inhibitors (chelerythrine chloride, polymyxin B, and phloretin) and activators (PMA and DAG) potentiate Ca2+ release from Ca2+-loaded retinal rod microsomes. Specific and nonspecific mechanisms of Ca-release stimulation by the modulators of PKC activity are discussed.