Calmodulin Antagonists Inhibit T-Type Ca2+ Currents in Mouse Spermatogenic Cells and the Zona Pellucida-Induced Sperm Acrosome Reaction

• Published in: Developmental biology 2001-08, Vol.236 (1), p.210-219
• Main Authors: López-González, Ignacio, De La Vega-Beltrán, Jose L., Santi, Celia M., Florman, Harvey M., Felix, Ricardo, Darszon, Alberto
• Format: Article
• Language: English
• Subjects: acrosome reaction; Ca2+ channel regulation; CaM; sperm; spermatogenic cells; T-type Ca2+ channel; TFP
• ISSN: 0012-1606; 1095-564X
• DOI: 10.1006/dbio.2001.0314

The sperm acrosome reaction (AR) is a regulated exocytotic process required for gamete fusion. It depends on an increase in [Ca2+]i mediated by Ca2+ channels. Although calmodulin (CaM) has been reported to regulate several events during the AR, it is not known whether it modulates sperm Ca2+ channels. In the present study we analyzed the effects of CaM antagonists W7 and trifluoroperazine on voltage-dependent T-type Ca2+ currents in mouse spermatogenic cells and on the zona pellucida-induced AR in sperm. We found that these CaM antagonists decreased T-currents in a concentration-dependent manner with IC50 values of ∼10 and ∼12 μM, respectively. W7 altered the channels' voltage dependence of activation and slowed both activation and inactivation kinetics. It also induced inactivation at voltages at which T-channels are not activated, suggesting a promotion of inactivation from the closed state. Consistent with this, W7 inhibited the ZP-induced [Ca2+]i transients in capacitated sperm. Likewise, W7 and TFP inhibited the AR with an IC50 of ∼10 μM. In contrast, inhibitors of CaM-dependent kinase II and protein kinase A, as well as a CaM-activated phosphatase, had no effect either on T-currents in spermatogenic cells or on the sperm AR. Together these results suggest a functional interaction between CaM and the sperm T-type Ca2+ channel. They are also consistent with the involvement of T-channels in the AR.