A dihydropyridine-sensitive t-type ca2+ current is the main ca2+ current carrier in mouse primary spermatocytes. Santi, Celia M., Alberto Darszon, and Arturo Hern[acute]andez-Cruz. Instituto de Fisiolog[acute]ia Celular, Universidad Nacional Aut[acute]onoma de M[acute]exico, Circuito Exterior, Ciudad Universitaria M[acute]exico City, D.F. 04510, M[acute]exico, and Instituto de Biotecnolog[acute]ia, UNAM, Cuernavaca, Mor., M[acute]exico
APStracts 3:0157C, 1996.
Ca2+ entry through Ca2+ channels is likely to play an important role in the differentiation of male germ cells as well as in fertilization by mature sperm. Here we present a detailed analysis of Ca2+ currents expressed in acutely dissociated mouse primary spermatocytes. Patch -clamp recordings demonstrated that the only voltage-gated Ca2+ channels present belong to the family of T-type Ca2+ currents. Accordingly, Ni2+ (200 [mu]M) and amiloride (500 [mu]M) reduced current amplitude by 75% and 62%, respectively. To our knowledge, this is the first report of a system where T-type Ca2+ channels are expressed in isolation. Unexpectedly, 5 and 10 [mu]M nifedipine also reduced peak currents by 38% and 53%, respectively. Significant inhibition of the Ca2+ current occurred at concentrations as low as 2 [mu]M. Since mature sperm cells are unable to synthesize new proteins, these Ca2+ channels are also likely to be present in these cells, where they may contribute to the Ca2+ influx required to trigger the acrosome reaction, This notion is supported by the fact that concentrations of nickel and nifedipine which block these Ca2+ currents, also inhibit the acrosome reaction. Since these channels represent the primary pathway for voltage-gated Ca2+ entry in mouse spermatocytes, they may also participate in regulating meiotic cell division and sperm differentiation. 

Received 19 March 1996; accepted in final form 3 May 1996.
APS Manuscript Number C157-6.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 28 May 96