T-type Ca2+ channels and alpha(1E) expression in spermatogenic cells, and their possible relevance to the sperm acrosome reaction

There is pharmacological evidence that Ca2+ channels play an essential role in triggering the mammalian sperm acrosome reaction, an exocytotic process required for sperm to fertilize the egg, Spermatozoa are small terminally differentiated cells that are difficult to study by conventional electrophysiological techniques. To identify the members of the voltage-dependent Ca2+ channel family possibly present in sperm, we have looked for the expression of the alpha(1A), alpha(1B), alpha(1C), alpha(1D) and alpha(1E) genes in mouse testis and in purified spermatogenic cell populations with RT-PCR. Our results indicate that all 5 genes are expressed in mouse testis, and in contrast only alpha(1E), and to a minor extent alpha(1A), are expressed in spermatogenic cells. In agreement with these findings, only T-type Ca2+ channels sensitive to the dihydropyridine nifedipine were observed in patch-clamp recordings of pachytene spermatocytes. These results suggest that low-threshold Ca2+ channels are the dihydropyridine-sensitive channels involved in the sperm acrosome reaction.