title: Voltage-operated Ca2+ channels and the acrosome reaction: which channels are present and what do they do?
abstract: Evidence from pharmacological studies suggests that induction of the acrosome reaction of mammalian spermatozoa by solubilized zona pellucida, and possibly by progesterone, is dependent upon Ca2+ influx through voltage-operated Ca2+ channels. Studies on Ca2+ accumulation and membrane potential in ligand-stimulated or artificially depolarized spermatozoa support such a conclusion. Electrophysiological studies on rodent spermatogenic cells have revealed the presence of a 'T' type voltage-operated Ca2+ current. This current has pharmacological attributes consistent with those of the putative channel responsible for Ca2+ influx mediating the acrosome reaction. However, use of molecular techniques to study human and rodent testis and spermatogenic cells has detected the presence of three different voltage-operated Ca2+ channel subunits. One of these (alpha lE) may generate T-currents, though this is currently disputed. Voltage-operated Ca2+ channel structure and the relationship between channel subunit expression and the characteristics of consequent Ca2+ currents is briefly reviewed. The nature and function of T-channel-mediated Ca2+ influx is examined in the context of the time-course of ligand- and depolarization-induced elevation of [Ca2+]i in mammalian spermatozoa. It is likely that a secondary Ca2+ response (mobilization of stored Ca2+ or activation of a second Ca(2+)-influx pathway) is required for the acrosome reaction. Evidence for the existence and participation of various candidates is discussed (including voltage-operated Ca2+ channels, which may be functionally expressed only in mature spermatozoa), the available evidence favouring a secondary Ca(2+)-influx pathway. Immediate priorities for future research in this area are proposed.
authors.affiliation: School of Biological Science, University of Birmingham, UK.
authors.forename: S J
authors.initials: SJ
authors.lastname: Publicover
authors.forename: C L
authors.initials: CL
authors.lastname: Barratt
mesh_terms: D020101:Acrosome Reaction / Q000502:physiology*; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000502:physiology*; D004594:Electrophysiology; D006801:Humans; D008297:Male; D013094:Spermatozoa / Q000502:physiology*
chemical_list: D015220:Calcium Channels; D002118:Calcium