Progesterone effect mediated by the voltage-dependent calcium channel and protein kinase C on noncapacitated cryopreserved bovine spermatozoa.

An increase in intracellular calcium is essential to trigger capacitation and the acrosome reaction. The aim of this study was to determine the progesterone effect mediated by the voltage-dependent calcium channel and protein kinase C on heparin-capacitated and noncapacitated spermatozoa. Protein kinase C was activated by 1-oleoyl-2-acetyl glycerol, a membrane-permeant diacyl-glycerol, and inhibited by GF-109203X. The percentage of true acrosome reaction was evaluated using differential-interferential optical contrast microscopy and trypan blue stain. The calcium concentration was evaluated by FURA-2AM and methoxyverapamil was used as a voltage-dependent calcium channel inhibitor. A rapid calcium increase and acrosome reaction were induced by progesterone in capacitated and noncapacitated spermatozoa, a higher intracellular calcium increase being observed in capacitated than in noncapacitated samples (P < 0.05). The calcium increase and acrosome reaction were blocked significantly by GF-109203X in noncapacitated and capacitated spermatozoa by the addition of progesterone and/or 1-oleoyl-2-acetylglycerol. Methoxyverapamil blocked calcium influx in samples treated with progesterone and heparin/progesterone, but not in those treated with 1-oleoyl-2-acetyl glycerol. Progesterone induces the acrosome reaction in noncapacitated cryopreserved bovine spermatozoa through intracellular mechanisms dependent on protein kinase C and the voltage-dependent calcium channel.