The morphology and size of spermatozoa hinder the study of the functional properties of the spermatozoa plasma membrane. However, some studies have revealed the presence of a number of ion channels in this cell. We set out to measure the endogenous currents and to study the effect of the venom of the Chilean black widow spider (Latrodectus mactans). By patch-clamping bovine spermatozoa our results indicate the presence of an outwardly rectifying current, sensitive to changes in K(+) concentration (30-140 mM) and to tetraethylammonium (TEA, 10-100 mM). The application of the venom (7.5 microg/ml) blocks these K+ currents and then alters the passive properties of the plasma membrane. This leads to the entry of Ca(++), reflected by a change in basal fluorescent units (5+/-2 at 35+/-10 FAU). The Ca(++) influx follows a reduction in the membrane conductance (control 22+/-2; venom 10+/-1 pS), as calcium channels open in accord with voltage dependence.
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