A ouabain-sensitive membrane conductance.

1. Changes in membrane conductance and potential of sodium-loaded frog muscle fibres were found when the external recovery solution was changed: from cold to warm, to warm plus ouabain, to cold plus ouabain. Comparisons of these measurements for different external solutions were made by leaving the electrodes implanted in the same fibre during all solution changes. (The recovery solutions contained 10 mM-K and 82 mM-Cl.)2. The membrane potential became more negative on warming, less negative when ouabain was added, and still less negative when the ouabain-containing recovery solution was cooled. The membrane conductance increased on warming, increased further on addition of ouabain, and decreased when the ouabain-containing recovery solution was cooled.3. The increase of conductance which occurred on warming decreased with increasing periods in cold recovery. The increase of conductance which occurred on addition of ouabain decreased if the ouabain was added to the recovery solutions of muscles which were more fully recovered.4. The ouabain-sensitivity of the membrane conductance may be dependent upon the sodium-pump rate, or the extent of recovery of the sodium-loaded muscle fibre in the potassium- and chloride-containing recovery solutions.5. It is suggested that if the potassium conductance of the membrane increases with decreasing sodium-pump rates, then during the initial part of the recovery period a non-electrogenic mechanism must be producing a substantial part of the early net potassium influx.