Title: Activation of mouse sperm T-type Ca2+ channels by adhesion to the egg zona pellucida.

Authors: C Arnoult, R A Cardullo, J R Lemos, H M Florman

Journal, date & volume: Proc. Natl. Acad. Sci. U.S.A., 1996 Nov 12 , 93, 13004-9

PubMed link: http://www.ncbi.nlm.nih.gov/pubmed/8917534

Abstract
The sperm acrosome reaction is a Ca(2+)-dependent exocytotic event that is triggered by adhesion to the mammalian egg's zona pellucida. Previous studies using ion-selective fluorescent probes suggested a role of voltage-sensitive Ca2+ channels in acrosome reactions. Here, wholecell patch clamp techniques are used to demonstrate the expression of functional T-type Ca2+ channels during mouse spermatogenesis. The germ cell T current is inhibited by antagonists of T-type channels (pimozide and amiloride) as well as by antagonists whose major site of action is the somatic cell L-type Ca2+ channel (1,4-dihydropyridines, arylalkylamines, benzothiazapines), as has also been reported for certain somatic cell T currents. In sperm, inhibition of T channels during gamete interaction inhibits zona pellucida-dependent Ca2+ elevations, as demonstrated by ion-selective fluorescent probes, and also inhibits acrosome reactions. These studies directly link sperm T-type Ca2+ channels to fertilization. In addition, the kinetics of channel inhibition by 1,4-dihydropyridines suggests a mechanism for the reported contraceptive effects of those compounds in human males.