Role of phosphatidylinositol in basal adenylate cyclase activity of rat heart sarcolemma.

The adenylate cyclase activity and phospholipid composition were determined in rat heart sarcolemma after treating the membranes with a phosphatidylinositol-specific phospholipase C. Complete hydrolysis of phosphatidylinositol in sarcolemma was associated with a marked loss of the basal adenylate cyclase activity. The recombination of the supernatant with the phosphatidylinositol-depleted membranes was found to reactivate the adenylate cyclase activity. The soluble component(s) in the supernatant, which restored the adenylate cyclase activity, was thermolabile and precipitated by ammonium sulfate. Extensive hydrolysis of phosphatidylcholine, phosphatidylethanolamine and sphingomyelin in sarcolemma with a Clostridium welchii phospholipase C treatment did not affect the basal adenylate cyclase activity. These results suggest that phosphatidylinositol anchors component(s) essential for the expression of basal adenylate cyclase activity to the myocardial cell membrane.