Intracellular chloride concentration and evidence for the existence of a chloride pump in frog skeletal muscle.

Intracellular chloride concentration in frog sartorius muscle was determined at 20 degrees C utilizing ionic permeability change of the membrane for an ion-selective electrode. The membrane potential and external potassium concentration relation was obtained with changes in pH. Using the constant field equation with a condition given by the crossing point in the two relations obtained with the two different pH, the intracellular chloride concentration was estimated to be 3.7 +/- 0.18 mM (mean +/- S.E.M.) with a 0.76 of the activity coefficient for chloride in Ringer's solution. The chloride potential (-88.5 +/- 1.26 mV) was significantly positive to the resting potential (-94.8 +/- 1.09 mV), suggesting that a chloride pump may be working in the frog skeletal muscle. The existence of the chloride pump was supported further by the fact that the depolarization induced by the pH increase became smaller with cooling and finally disappeared when cooled below 5 degrees C.