Measurement of cation fluxes in rat diaphragm

Abstract

Calculation of the ionic flux in isolated mammalian muscle at 38° C required a knowledge of internal ion concentration, the cell dimensions, and the kinetics of exchange across the cell membrane. Muscles soaked in Krebs saline showed no indication of fibre swelling or gain of cell water; there was a small fall of intracellular potassium, accompanied by a large rise of sodium. With proper oxygenation, muscle potassium was constant for several hours; anoxia rapidly produced a fall in potassium and gain of sodium. The use of radioactive tracers showed that potassium was completely exchangeable. The mean half-time for exchange of potassium between tissue and saline was 45 min. Initially the rate was somewhat more rapid, but it finally became steady. There was no significant difference between the rates of entry and exit. Potassium exchange was apparently slowed by diffusion through the inter­spaces; the calculated exchange rate across the cell membrane had a half-time of 36 min. The mean potassium flux, after correcting for diffusion, was 21 x 10 -12 equiv. cm -2 s -1 . Fibre sodium exchanged with a half-time of about 10 min, and the outward sodium flux was 28 x 10 -12 equiv. cm -2 s -1 . High values were found for the intercellular space, being 26 ml./100 g in soaked diaphragm muscles as measured by inulin. This was confirmed by a method involving radioactive sodium, and the inulin space in vivo was similar. In their passage through the intercellular fluid, inulin, potassium and sodium appear to follow simple diffusion kinetics, and their apparent diffusion coefficients have been estimated.