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

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Abstract
1. Frog sartorii and toe muscles were loaded in a 100 m M‐K 216 m M‐Cl solution at pH 7·4 labelled with either 36Cl, or 42K, 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 36Cl into acid solution was extremely slow so that the cellular fraction could easily be distinguished. On raising the pH the efflux of 36Cl 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 42K from sartorii was only slightly increased by alkaline solutions. When the effluxes of 36Cl and 42K were measured simultaneously the increment in chloride efflux was much greater than the increment in 42K efflux.4. Toe muscles depolarized by high potassium solution showed an approximately twofold increase in 42K 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.