Decrease in calmodulin concentrations during heparin-induced capacitation in bovine spermatozoa.

Concentrations of the intracellular Ca(2+)-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 4-6 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 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.