INTERACTION OF K+ OUABAIN AND NA+ ON CATION TRANSPORT AND RESPIRATION OF RENAL CORTICAL CELLS ON HAMSTERS AND GROUND SQUIRRELS

1. 1. The interactions of K+ and ouabain on kidney cell respiration and Na+ extrusion were studied. The influence of intracellular Na+ on kidney cell respiration was compared with its effect on K+ transport. 2. 2. Omission of K+ from the medium in which kidney slices are incubated causes a reduction in Na+ extrusion and respiration comparable to that caused by maximal ouabain inhibition. 3. 3. The effect of ouabain in K+-free medium on respiration, Na+ extrusion and tissue K+ concentration is greatly enhanced over its effect in the presence of K+. Na+ extrusion is virtually blocked; tissue K+ falls to extraordinarily low concentrations. In hamster kidneys which are normally insensitive to ouabain the sensitivity to low concentrations of ouabain is increased in the absence of K+. 4. 4. At 5° the omission of K+ from the medium has a slight effect on respiration in slices of kidneys of ground squirrels but not in those of hamsters. The combined effecs of K+ removal and ouabain on Na+ extrusion at 5° are similar to those at 38°. 5. 5. Slices of hamster kidney loaded with Na+ and incubated with Na+ respire more rapidly at 5° than slices leached of Na+ and incubated in Na+-free medium. 6. 6. Na+-loaded slices in Na+-free medium also have a high O2 consumption relative to slices with no Na+, showing that it is intracellular Na+ that stimulates respiration. Slices loaded with 30 mM Na+ and incubated in Na+-free medium at 5° respired at a rate midway between that of Na+-rich and Na+-depleted slices. This finding is in accord with the fact that the rate of K+ transport from slices loaded with 30 mM Na+ is also half-maximal. 7. 7. The findings with regard to K+, ouabain and Na+ effects on respiration and transport are discussed in terms of four recently suggested hypotheses. It is concluded that on the basis of available evidence the results may be best explained by the existence of long diffusion pathways between the site of the cation pump and the external medium. 8. 8. It is further concluded that while tissue respiration is governed partly and specifically by the rate of total Na+ transport, it is difficult to obtain a truly basal, non-transport related metabolism. This may also be because of the existence of local pools of cation in the vicinity of the pump activation sites. © 1968.