SIGNAL-TRANSDUCTION BY THE PHOSPHATIDYLINOSITOL CYCLE IN MYOCARDIUM

Diverse and distinct hormonal stimuli arriving at the cardiomyocyte en gage specific surface receptors to initiate hydrolysis of inositol pho spholipids by phospholipase C whereby information flows from changes i n intracellular levels of inositol 1,4, 5-trisphosphate and inositol 1 ,3,4,5-tetrakisphosphate, 1,2-diacylglycerol and Ca2+ to the specific phosphorylation of cellular proteins by various protein kinases such a s the protein kinase C family, Ca2+-calmodulin-dependent kinase and mi togen activated kinases. The phosphorylation products are potential re gulators of the inotropic and chronotropic state, hypertrophic growth and specific gene expression and ischemic preconditioning of the myoca rdium, This review summarizes the current state of knowledge concernin g the phosphatidylinositol cycle and its potential role in mediating v arious functional responses in myocardium. The multiplicity of recepto r types, G-proteins, phospholipases C and protein kinases raises funda mental questions about the mechanisms that assure the precision and ti ming of the myocardial response to hormonal stimuli.