Nongenomic steroid action: independent targeting of a plasma membrane calcium channel and a tyrosine kinase.

It is known that steroids can produce nongenomic effects on cells, such as opening of ionic channels, membrane receptor aggregation or changes in protein phosphorylation status. However, it is not known whether these different effects, when occurring concomitantly, are linked by a causal relationship or whether they are triggered independently by the steroid ligand. Here we show that progesterone opens a plasma membrane Ca2+ channel and activates a protein tyrosine kinase of human spermatozoa independently of each other because, on the one hand, tyrosine kinase inhibition does not affect the progesterone-induced Ca2+ influx and, on the other hand, the absence of extracellular Ca2+ does not preclude tyrosine-kinase-mediated progesterone-induced acrosomal exocytosis. These data suggest that steroids interact with multireceptor systems on the surface of responsive cells.