ASSOCIATION OF PHOSPHOLIPASE C-DELTA WITH A HIGHLY ENRICHED PREPARATION OF CANINE SARCOLEMMA

Myocardial synthesis of phosphatidylinositol 4,5-bisphosphate (PIP2) is highly compartmentalized in the sarcolemmal membrane. Sarcolemmal vesicles contain endogenous phospholipase C (PLC), but the identity of sarcolemmal PLC and its relationship to soluble PLC have not been determined previously. Sarcolemmal and cytosolic PLC were prepared from canine myocardium and characterized by DEAE-cellulose chromatography and by immunoblotting with monoclonal and polyclonal antibodies to isoenzymes of PLC (PLC(beta), PLC(gamma), and PLC(delta). DEAE-cellulose chromatography resolved two forms of cytosolic PLC that were identified as an 85-kDa form of PLC(delta) and a 145-kDa form of PLC(gamma). In contrast, DEAE-cellulose chromatography resolved a single form of sarcolemmal PLC that was identified as an 85-kDa form of PLC(delta). These data demonstrate that PLC, and PLC(delta) are expressed in canine myocardium and that an 85-kDa form of PLC(delta) is selectively associated with sites of PIP2 synthesis in a highly enriched preparation of sarcolemma. These data do not exclude the existence of additional isoenzymes of sarcolemmal PLC that may have been removed during isolation of sarcolemmal membranes.