Differential modulation by protein kinase C of progesterone-activated responses in human sperm

Progesterone exerts important effects on human spermatozoa by rapid non genomic mechanisms of action. It has been demonstrated that processes triggered by this steroid are dependent on the activation of calcium influx through the plasma membrane. Beside calcium, progesterone also induces a rapid plasma membrane depolarization that is dependent on an influx of sodium through a putative progesterone-activated channel located on the plasma membrane. In this study we show that protein-kinase C inhibition inhibits calcium influx activated by progesterone, while leaving the depolarizing effect of this steroid unchanged. These results may be explained by the existence of two progesterone receptors on human sperm plasma membrane, one responsible for calcium influx and modulated by protein-kinase C and the other selectively permeable to sodium that is not under protein-kinase C control. Alternatively, protein-kinase C inhibition might change ion selectively of a single progesterone-activated channel, thus decreasing calcium permeability, while leaving sodium permeability unchanged.