EFFECT ON SPERM-INDUCED ACTIVATION CURRENT AND INCREASE OF CYTOSOLIC CA2+ BY AGENTS THAT MODIFY THE MOBILIZATION OF [CA2+](I) .1. HEPARIN AND PENTOSAN POLYSULFATE

The mechanism of the elevation of intracellular free Ca2+ ([Ca2+](i)) induced by a single sperm in eggs of the sea urchin Lytechinus variega tus was investigated. Simultaneous measurements of [Ca2+](i), and of t he activation current, were carried out on eggs microinjected with Ca Green-1 or Ca Green dextran, and voltage clamped at -20 mV. The microi njection of 0.5 to 1.0 mg/ml heparin (MW 6000) or pentosan polysulfate (MW 3000), final intracellular concentration, causes a concentration- dependent inhibition in all parameters of the sperm-induced elevation of [Ca2+](i) and the phase 2 calcium-activated cation current (I-p). F or each: (1) the onset is delayed; (2) the rate of change is slowed; a nd (3) the peak amplitude attained is diminished. In some experiments at the higher concentrations, the microinjected polysulfates cause the complete suppression of the sperm-induced elevation of [Ca2+](i) and I-p. The entry of multiple sperm overcomes the inhibitory effects of t he polysulfates. Our data suggest that inositol 1,4,5-trisphosphate is the primary mechanism responsible for the sperm-induced release of Ca 2+ from intracellular stores. (C) 1995 Academic Press, Inc.