Anion channel blockers differentially affect T-type Ca2+ currents of mouse spermatogenic cells, a1E currents expressed in Xenopus oocytes and the sperm acrosome reaction
Por:
Espinosa F., López-González I., Serrano C.J., Gasque G., De La Vega-Beltrán J.L., Treviño C.L., Darszon A.
Publicada:
1 ene 1999
Resumen:
The direct electrophysiological characterization of sperm Ca2+ channels has been precluded by their small size and flat shape. An alternative to study these channels is to use spermatogenic cells, the progenitors of sperm, which are larger and easier to patch-clamp. In mouse and rat, the only voltage-dependent Ca2+ currents displayed by these cells are of the T type. Because compounds that block these currents inhibit the zona pellucida-induced Ca2+ uptake and the sperm acrosome reaction (AR) at similar concentrations, it is likely that they are fundamental for this process. Recent single channel recordings in mouse sperm demonstrated the presence of a Cl- channel. This channel and the zona pellucida (ZP)-induced AR were inhibited by niflumic acid (NA), an anion channel blocker [Espinosa et al. (1998): FEBS Lett 426:47-51]. Because NA and other anion channel blockers modulate cationic channels as well, it became important to determine whether they affect the T-type Ca2+ currents of spermatogenic cells. These currents were blocked in a voltage-dependent manner by NA, 1,9- dideoxyforskolin (DDF), and 5-nitro-2-(3-phenylpropylamine)benzoic acid (NPPB). The IC50 values at -20 mV were 43 ?M for NA, 28 ?M for DDF, and 15 ?M for NPPB. Moreover, DDF partially inhibited the ZP-induced AR (40% at 1 ?M) and NPPB displayed an IC50 value of 6 ?M for this reaction. These results suggest that NA and DDF do not inhibit the ZP-induced AR by blocking T-type Ca2+ currents, while NPPB may do so. Interestingly 200 ?M NA was basically unable to inhibit ?1E Ca2+ channels expressed in Xenopus oocytes, questioning that this ? subunit codes for the T-type Ca2+ channels present in spermatogenic cells. Evidence for the presence of ?1C, ?1G, and ?1H in mouse pachytene spematocytes and in round and condensing spermatids is presented.
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