Regulation of [ 3H]nitrendipine binding by phospholipases A 2 and C through direct and GTP-sensitive mechanisms

Abstract

We compared the effects of Phospholipases A 2, C, B and D on [ 3H]nitrendipine binding to hamster cardiac membranes, in the absence and presence of ATP or GTP. Phospholipase A 2, competitively inhibited [ 3H]nitrendipine binding to hamster cardiac membranes unchanged by ATP or GTP (K i = 5 ng/ml); as evidenced by complete and reversible displacement of [ 3H]nitrendipine binding and increase in K D on Scatchard analyses. Phospholipase C also completely inhibited [ 3H]nitrendipine binding to hamster cardiac membranes (K i = 5 ug/ml) with a decrease in B max and no change in K D on Scatchard analyses. The addition of GTP alone inhibited the PLC effect in EGTA-treated membranes. The addition of GTP with either CaCl 2, or ATP or both resulted in an equal and opposite enhancement of the PLC effect. Phospholipases B and D had no effect on [ 3H]nitrendipine binding. These data support: (1) Direct effect of PLA 2 on dihydropyridine binding. (2) Indirect regulation of dihydropyridine binding by Phospholipase C through a GTP and ATP-sensitive mechanism.