Acrosome reaction of human spermatozoa is mainly mediated by alpha1H T-type calcium channels

The objectives of this study were: (i) to investigate the possible role of T-type Ca(2+) channels on the acrosome reaction (AR) of human spermatozoa; and (ii) to determine the sub-type of T-type calcium channels involved in the AR. The AR was induced in vitro by mannose-bovine serum albumin (BSA). The inhibitory effects of mibefradil (T-type Ca(2+) channel blocker), NiCl(2), or nifedipine (L-type Ca(2+) channel blocker) on the mannose-BSA induced AR were evaluated in capacitated human spermatozoa. The AR was sensitively inhibited by low micromolar concentrations of mibefradil (IC(50) = 1 micromol/l) in a dose-dependent manner. Low concentrations of Ni(2+) (IC(50) = 40 micromol/l) also inhibited the mannose-BSA induced AR. On the contrary, higher concentrations of nifedipine were required to block AR (IC(50) = 60 micromol/l). Reverse transcription-polymerase chain reaction (RT-PCR) was performed to identify the sub-types of T-type channels present in human testes. Analysis of PCR products showed that only alpha1H subunits are expressed in testes. The expression of the alpha1H subunit may be tissue specific since its mRNA was not detected in the human ovary. The present study suggests that the AR of human spermatozoa is highly associated with T-type Ca(2+) channels and is mainly mediated by calcium influx through alpha1H T-type Ca(2+) channels.