“…The relatively high steady‐state chloride conductance, g Cl , of frog skeletal muscle fibre membranes, which is important for stabilization of the resting membrane potential, is strongly dependent on external pH. Cl − exchange under conditions of Cl − equilibrium in depolarized fibres (Skydsgaard, 1987) and g Cl in both normal (∼120 mM Cl − ) and high‐KCl Ringer solution (Hutter & Warner, 1967 a ) are all inactivated in acid medium with an apparent p K of ∼7 in Rana temporaria , possibly due to the protonation of histidines in the Cl − channels (Hutter & Warner, 1967 a,b ; Spalding, Taber, Swift & Horowicz, 1991). The acidification reduces g Cl more than it reduces the Cl − flux and there is evidence that a considerable fraction of the residual flux at low pH may be non‐conductive, possibly taking place via exchange diffusion (Harris, 1965; Hutter & Warner, 1967 b ; Skydsgaard, 1987).…”