The effect of pH on the 36-Cl efflux from frog skeletal muscle.

1. Frog sartorii and toe muscles were loaded in a 100 mM-K 216 mM-Cl solution at pH 7.4 labelled with either (36)Cl, or (42)K, or with both isotopes. The efflux of the isotopes into inactive solution of the same composition at pH 5.0 and 9.8 was followed.2. The efflux of (36)Cl into acid solution was extremely slow so that the cellular fraction could easily be distinguished. On raising the pH the efflux of (36)Cl from sartorii increased 4.5 +/- 0.43 (mean +/- S.E.) times; from toe muscles 6.7 +/- 0.69 (mean +/- S.E.) times. The effect was fully reversible.3. The efflux of (42)K from sartorii was only slightly increased by alkaline solutions. When the effluxes of (36)Cl and (42)K were measured simultaneously the increment in chloride efflux was much greater than the increment in (42)K efflux.4. Toe muscles depolarized by high potassium solution showed an approximately twofold increase in (42)K efflux on transfer from acid to alkaline solution. This effect was independent of the presence of chloride ions.5. The results confirm the identification of chloride as the ion species principally concerned in the pH sensitivity of the membrane conductance.