Amiloride or the reduction of external Na⁺ blocks most P_Na, leaving the membrane dominated by P_K.

Abstract

<p>Amiloride treatment (A) and low external Na⁺ (B) leave the sperm membrane dominated by P_K in both wild-type and in SLO3 mutant sperm. After the addition of amiloride the P_K to P_Na ratio is somewhat larger in wild-type than in the SLO3 mutant, reflecting the activity of SLO3 K⁺ channels in the membrane (see text). Although the SLO3 channel is absent in SLO3 mutant sperm, the dominance of P_K over all other ion permeabilities in SLO3 mutant sperm is additional evidence for the presence of a K⁺ leak conductance in SLO3 mutant sperm plasma membrane. GHK fits did not require inclusion of P_Cl (see text). Since we cannot accurately predict the internal sodium concentration when external Na⁺ is reduced to 1 mM, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0060578#pone-0060578-g006" target="_blank">figure 6B</a> is fitted with least squares linear regression to compare the resulting slopes with that of a theoretical line illustrating pure potassium selectivity (red). Permeability values predicted by the GHK equation for A are given in (C). The curves correspond to mean n = 4 experiments ± S.E.M. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0060578#pone.0060578.s010" target="_blank">table S6</a> for membrane potential values.</p