Effect of osmolality on renal medullary Na-K-ATPase activity in the postobstructive kidney.

The aim of this study was to determine the effect of changes in osmolality on the reduced renal medullary Na-K-ATPase (EC 3.6.1.3) activity of the postobstructive kidney. The effect of osmolality on renal medullary Na-K-ATPase activity was studied by incubating tissue slices from sham-operated and bilaterally obstructed rats in media with osmolality varied before enzyme isolation using sodium chloride, choline chloride, or sucrose. Both sham-operated and bilaterally obstructed rat renal medullary enzyme showed a similar increase in activity with increased osmolality due to sodium chloride. Medullary Na-K-ATPase from the postobstructive kidney also showed increased activity with osmotic changes induced by choline chloride or sucrose. It is proposed that the decrease of Na-K-ATPase activity observed after bilateral ureteral obstruction is due, at least in part, to the loss of the solute concentration gradient in the kidney.