Effect of external sodium on net potassium uptake by frog muscle

When longitudinal strips of frog stomach muscle or frog sartorius muscles, previously depleted of K by overnight immersion in the cold in K-free Ringer solution containing 116 mEq Na/liter, were reimmersed at room temperature in solutions containing K, replacement of Na in the recovery fluid by Li or choline inhibited net K uptake by the fibers. Stomach muscles soaked overnight in Na-free solutions containing Li or choline lost K and most of their Na, the Na being replaced by Li and, inferentially, by choline. When these muscles were reimmersed in Na-Ringer solution they accumulated K from the medium. On reimmersion in Na-free Li or choline-Ringer solution no net K uptake occurred. Partial replacement of Li or choline by Na resulted in net K accumulation. Stomach muscles soaked in K-free Na-Ringer solution and subsequently transferred to Na-free solutions containing Cs and K did not accumulate K. Partial replacement of Cs by Na did not affect the inhibition of K uptake by Cs. K accumulation by frog stomach muscle was not affected by cyanide (2 mmoles/liter). These results are compatible with a specific stimulating effect of external Na on K accumulation in frog muscle.

Sodium, potassium, and chloride in frog stomach muscle

In freshly excised stomach muscles of Rana temporaria total Na was found to be 40.2 ± 6.1 mEq/kg wet wt. Total K was 66.5 ± 4.8 and total Cl was 33.9 ± 3.9 mEq/kg. Total water content was 805 ± 16 g/kg and inulin space was 341 ± 52 ml/kg. The average intrafiber concentrations calculated from these data were 10 mEq Na, 141.5 mEq K, and 18 mEq Cl/ liter fiber water. In muscles immersed overnight at 5 C in Ringer's solutions containing various amounts of KCl, total muscle Cl was a direct linear function of external KCl. When the external KCl concentration was less than 20 mm/liter, muscle K decreased on immersion. Increasing the external KCl from 20 to 40 mm/liter resulted in a sharp increase in muscle K. Further increasing external KCl from 40 to 80 mm/liter had relatively little effect on total muscle K. The Na content of these muscles was in all cases greater than that of freshly excised muscles. Muscles immersed overnight in the cold in K-free solutions gained Na and lost K. On reimmersion at room temperature in solutions containing KCl there was a net loss of Na from and a net gain of K by the fibers. The amount of K taken up was a function of the external KCl concentration. Na loss and K accumulation were inhibited by ouabain and by iodoacetate.