A DUAL EFFECT OF SODIUM ON OXYGEN CONSUMPTION IN TOAD BLADDER

1. 1. QO2 measured in a Warburg respirometer was found to be stimulated by the addition of external Na+. The relationship between extra QO2 and the concentration of Na+ displays saturation kinetics, the maximal effect occurring at 40-60 mM. 2. 2. 2,4-Dinitrophenol stimulated QO2 and inhibited the short-circuit current (s.c.c.). The maximally effective concentration of dinitrophenol was the same for both, 5·10-5-10·10-5M. 3. 3. The addition of Na+ (40 mM) in the presence of dinitrophenol (1·10-4M) produced a further marked stimulation of QO2. The effects of varying the concentration of dinitrophenol on this Na+-independent QO2 paralleled the effects on s.c.c. and Na+-independent QO2. 4. 4. The results are interpreted as showing a direct stimulation of the respiratory chain by Na+ per se. © 1969.