Figure 20.

A: Conductances of the PA₆₃, C2IIa, and Ib channels as functions of salt concentrations demonstrate different behaviors at small salts. The dependences are close to linear for Ib but show significant deviations from linearity for the PA₆₃ and C2IIa channels. B: Single channel reversal potentials as functions of the ratio of salt concentrations on the different sides of the membrane for two series of measurements with oppositely directed gradients. Open circles: Reversal potential (E_rev) obtained in the series of experiments where KCl concentration in the cis compartment exceeds that in the trans compartment; at that c_trans = 0.1 M KCl. Solid circles: The values of the reversal potential (-E_rev) obtained for the reversed gradient c_trans > c_cis = 0.1 M KCl. The sign of the reversal potential is inverted in the latter case to facilitate comparison; the selectivity stays cationic in both cases. The channels are asymmetric because the absolute value of the reversal potential is greater when the more concentrated solution is on the cis side of the membrane. Membranes were formed from the DPhPC at pH 6.