EFFECTS OF PROTEIN-KINASE-C ACTIVATION ON INTRACELLULAR CA2+ DISTRIBUTION IN VASCULAR SMOOTH-MUSCLE CELLS OF SPONTANEOUSLY HYPERTENSIVE RATS

Protein kinase C is known to influence contraction in vascular smooth muscle cells by Ca2+-dependent and Ca2+-independent mechanisms. In the present study, the effect of protein kinase C activation by phorbol 12-myristate 13-acetate on resting cytosolic free Ca2+ and on cellular Ca2+ pools was assessed in cultured rat aortic muscle cells using fura 2. Cellular Ca2+ pools were evaluated with the selective inhibitor of the sarcoplasmic Ca2+ ATPase, thapsigargin. In normotensive vascular smooth muscle cells, protein kinase C activation caused a redistribution of Ca2+ from the thapsigargin-sensitive pool into the cytoplasm, whereas, in hyper-tensive cells, no significant effect of protein kinase C activity on cellular Ca2+ distribution was found. It is concluded that protein kinase C modulates the amount of Ca2+ stored in the thapsigargin-sensitive calcium stores. In hypertensive cells, the regulation of Ca2+ pools by protein kinase C is disturbed.