Regulation of membrane-associated iPLA₂ activity by a novel PKC isoform in ventricular myocytes

Thrombin stimulation of rabbit ventricular myocytes increases membrane-associated, Ca²⁺-independent phospholipase A₂ (iPLA₂) activity, resulting in accelerated hydrolysis of membrane plasmalogen phospholipids and increased production of arachidonic acid and lysoplasmenylcholine. This study was designed to investigate the signal transduction pathways involved in activation of membrane-associated iPLA₂. Incubation of isolated membrane fractions suspended in Ca²⁺-free buffer with thrombin or phorbol 12-myristate 13-acetate resulted in a two- to threefold increase in iPLA₂ activity. Prior treatment with the PKC inhibitor GF-109203X blocked iPLA₂ activation by thrombin. These data suggest that a novel PKC isoform present in the membrane fraction modulates iPLA₂ activity. Immunoblot analysis revealed a significant portion of PKC-ε present in the membrane fraction, but no other membrane-associated novel PKC isoform was detected by this method. These data indicate that activation of membrane-associated iPLA₂ is mediated by a membrane-associated novel PKC isoform in thrombin-stimulated rabbit ventricular myocytes.