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 μM 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.