Concentrations of the intracellular Ca2+-mediator calmodulin (CaM), were measured by radioimmunoassay during heparin-induced capacitation of bull spermatozoa. Heparin reduced sperm CaM concentrations in a dose-dependent manner corresponding with an increase in in-vitro fertilization rates. Such reductions were observed after heparin treatment for 4\p=n-\6 h, which is in agreement with the length of the capacitation period in bulls and was concomitant with an increase in CaM concentration in the

more »

... incubation medium, suggesting translocation of CaM from the spermatozoa to the surrounding milieu. This CaM translocation was inhibited partly by the protease inhibitor benzamidine, suggesting a role for the sperm protease in this process.