Cooperative thermal effects on the accumulation of potassium and sodium in frog muscle.

Sodium-rich frog muscles are found to extrude sodium and reaccumulate potassium at 0 degrees C. The uptake of potassium by these muscles is studied at three different temperatures as a function of external potassium concentration, K(ex). The steady-state potassium content of the tissue is related to K(ex). by a sigmoidal cooperative curve at all temperatures. These results are compared with findings on a mammalian smooth muscle.