Potassium increases intracellular calcium simulating progesterone action in human sperm

Progesterone (P) and zona pellucida are known to induce acrosome reaction i n human sperm by increasing cytosolic calcium. High concentrations of potas sium ions (K+) improve the rate of acrosome reaction in human sperm in vitr o. This article determined whether the effect of K+ on the acrosome in huma n sperm is mediated by increasing intracellular calcium ([Ca2+]i). The effe ct of K+ on [Ca2+]i was examined by using Fura 2 as the fluorescent indicat or. The effect of K+ and P on [Ca2+]i in sperm and the involvement of ion c hannels was compared. Motile sperm were collected by the swim-up method fro m semen of healthy volunteers and capacitated overnight in BWW containing 0 .5% BSA. Incubation of capacitated sperm with different concentrations of p otassium chloride (1.25-20 mM) resulted in dose-dependent increase in [Ca2]i similar to that observed with P. The increase in [Ca2+]i by K+ and P was blocked by the addition of EGTA, a Ca2+ chelator. K+-induced change in [Ca 2+] was not altered by the addition of dihydropyridine derivatives. The com bined treatment of K+ (20 mM) and P (0.75 mu g/mL) caused an additive effec t on the increase in [Ca2+]i. It would appear that human sperm plasma membr ane possess different Ca2+ channels responsive to P and K+.