INHIBITION OF CARDIAC SARCOLEMMAL SODIUM-CALCIUM EXCHANGER BY GLYCEROPHOSPHOINOSITOL 4-PHOSPHATE AND GLYCEROPHOSPHOINOSITOL 4-5-BISPHOSPHATE

The enrichment in phosphatidylinositol 4-phosphate and phosphatidylinositoI 4-5-bisphosphate of cardiac sarcolemmal vesicles stimulate Na+/Ca2+ exchange activity. On the contrary the deacylation products of polyphosphoinositides are powerful inhibitors of Na+/Ca2+ exchange: half maximal inhibition of 1.6 and 2.1 mu M have been observed for glycerophosphoinositol 4-phosphate and glycerophosphoinositol 4-5-bisphosphate, respectively. The data indicate a bidirectional regulation of Na+/Ca2+ exchanger and suggest that phosphorylated glycerophosphoinositoIs can be regarded as novel signal transducers of intracellular Ca2+ regulation in heart cell. (C) 1995 Academic, Inc.