VERAPAMIL DECREASES LYMPHOCYTE PROTEIN-KINASE-C ACTIVITY IN HUMANS

To determine if clinically used doses of the calcium antagonist verapa mil measurably alter intracellular transduction mechanisms associated with the phosphatidylinositol pathway, lymphocyte protein kinase C act ivity was determined in subjects in a drug-free state, after 1 week of verapamil treatment (120 mg three times daily) and after a second wee k of verapamil treatment (240 mg sustained-release preparation once da ily). Nine healthy male volunteers were studied and in these subjects baseline protein kinase C activity (mean +/- SEM; 5.07 +/- 0.76 pmol/m u g protein/min) tended to decrease after 1 week (3.50 +/- 0.20 pmol/m u g protein/min) and was significantly decreased after 2 weeks (3.14 /- 0.27 pmol/mu g protein/ min; p < 0.05 from baseline) of verapamil t reatment. These data indicate that verapamil, at usual clinical doses, decreases protein kinase C activity in a marker tissue, the circulati ng lymphocyte. If protein kinase C activity in this tissue is a surrog ate for other verapamil target tissues, such as vascular smooth muscle and heart muscle, these findings may provide insight into the in vivo mechanism by which verapamil decreases protein synthesis, limits cell growth, and reverses cellular hypertrophy in these tissues.