Calcium-dependent polyphosphoinositide hydrolysis is associated with exocytosis in vitro.

Micromolar calcium ions stimulate both exocytosis and polyphosphoinositide hydrolysis in sea urchin egg plasma membrane in vitro. Strontium and barium ions also stimulate both processes equally. Magnesium ions reduce the calcium sensitivity of both. Neomycin, a drug which prevents phosphoinositide hydrolysis, inhibits exocytosis in vitro. We suggest that hydrolysis of plasma membrane phosphoinositides may be an essential step in the fusion of the secretory granule and plasma membranes.