Relations between potassium and sodium levels in mammalian muscle and blood plasma

Abstract

Na which had entered the muscle fibers of rats after a period of K deprivation was slowly extruded when the rats were placed on a diet rich in K. The mean half period of extrusion, even with the plasma K above the normal level after 24 hr., was about 3 days. The muscle K, which had fallen to levels of 75-82 mmol./kg. on the avg., was fully restored to normal values (about 100 mmol./kg.) after 1 day on the high K diet, and did not appreciably change from this when the plasma concn. reached 9 mmol./kg. Considerable variability was shown by individual rats in the amounts of Na which had entered the muscle fibers during K deprivation. Examination of the data of Heppel for the rate of mixing of labelled ions with the Na which had entered the fibers during the low K period shows that the true entrance rate of K/unit concn. into such fibers is about 30 x as great as that of Na. The relative rate of passage of K ions.into the normal fibers may be far greater than this, as evidenced by the comparatively very slow extrusion of muscle Na, and it is also possible, as suggested by Ussing that the rate of mixing of the labelled ions may give values which are too high for ion transport.