Inhibitory action of cyclic AMP on inositol 1,4,5-trisphosphate-induced Ca2+ release in saponin-permeabilized platelets.

Ca2+ release triggered by inositol 1,4,5-trisphosphate (IP3) has been measured in saponin-permeabilized human platelets with quin2 or 45Ca2+. Ca2+ was sequestered by intracellular organelles in the presence of ATP, and IP3 released half of the sequestered Ca2+. The addition of cyclic AMP (cAMP) to permeabilized platelets transiently accelerated Ca2+ sequestration, but did not alter the steady-state level. In contrast, IP3-induced Ca2+ release was greatly inhibited by cAMP. Phorbol myristate acetate, an activator of protein kinase C did not affect IP3-induced Ca2+ release. These results indicate that cAMP may be involved in the regulation of IP3-induced Ca2+ release in human platelets.