Calcium and Potassium Uptake from Sodium Free Media by Frog Stomach Muscle. ∗

Abstract

Summary and Conclusions

Isolated strips of frog stomach muscle, previously immersed overnight at 5°C in Na⁺ free Ringer solutions containing 110 mEq Li⁺, 6 mEq K⁺, and 1.8 mEq Ca⁺⁺/1 accumulated K⁺ when reimmersed in a solution containing 106 mEq Na⁺, 10 mEq K⁺ and 1.8 mEq Ca⁺⁺/1. When Na⁺ was replaced by Li⁺ in the second immersion fluid, K⁺ accumulation was inhibited. Removal of Ca⁺⁺ from the Li⁺ Ringer used for the second immersion did not significantly increase the uptake of K⁺ by the fibers. Muscles kept in Ca⁺⁺ free Li⁺ Ringer during both immersions had a significantly lower K⁺ content than muscles immersed throughout in Li⁺ Ringer containing 1.8 mM Ca^{+ +} . Increasing the Ca⁺⁺ content of the fluid used for the second or for both immersions had no significant effect on the final K⁺ content of muscles kept throughout the experiment in media containing normal concentrations of Na⁺. It is concluded that the inhibition of K⁺ uptake by frog stomach muscle observed when Na⁺ is replaced by Li⁺ in the second immersion medium does not arise from metabolic disturbances caused by an increased entry of Ca^{+ +} into the fibers.