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 exocytot ic process required for sperm to fertilize the egg, Spermatozoa are sm all terminally differentiated cells that are difficult to study by con ventional electrophysiological techniques. To identify the members of the voltage-dependent Ca2+ channel family possibly present in sperm, w e 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 sperm atogenic 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 record ings of pachytene spermatocytes. These results suggest that low-thresh old Ca2+ channels are the dihydropyridine-sensitive channels involved in the sperm acrosome reaction.