Ion channels from the mouse sperm plasma membrane in planar lipid bilayers

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Abstract
Fusion of purified mouse sperm plasma membranes to planar lipid bilayers resulted in the insertion of three ion channel types. They could be discerned on the basis of their selectivity, conductance, gating and voltage-dependent properties. The presence of a previously reported large, Ca2+-selective channel was confirmed. Here, it is reported that the Ca21-selective channel from mouse sperm plasmamembrane displayed a pNa+/Pk+= 1.6 ± 0.2(n=4) and was blocked by micromolar concentrations of ruthenium red. Fusion yielded also a cation-selective channel (PNa+/Pk+= 2.5±0.3,n=3) with a main open conductance substate of 103 pS and a smaller open substate of 51 PS(600mM K+cis/100 mM Na+trans). The channel inserted into bilayers in two stable fashions: a high-activity mode (open probability = 0.57 ± 0.02, n=3), and a low activity mode (open probability cis/100KCItrans), was identified. It displayed a high, nearly constant open probability (∼0.90)in the 0 to –80 mV range.