Renal adaptation to potassium in the adrenalectomized rabbit. Role of distal tubular sodium-potassium adenosine triphosphatase.

Potassium secretion and sodium-potassium adenosine triphosphatase (Na-K-ATPase) activity in the distal nephron segments are known to be influenced by the dietary intake of K+. This has been attributed to a change in the plasma aldosterone level, which also influences K+ secretion and Na-K-ATPase activity in the distal nephron. To investigate whether or not dietary K+ can modulate Na-K-ATPase activity in the distal nephron independently of aldosterone, we determined Na-K-ATPase activity in four distinct nephron segments of adrenalectomized (adx) rabbits given four specific diets for 1 wk before experimentation. Na-K-ATPase activity was determined by a fluorometric microassay in which ATP hydrolysis is coupled to NADH oxidation. The nephron segments examined were the distal convoluted tubule (DCT), the connecting tubule (CNT), the cortical collecting duct (CCD), and the outer medullary collecting duct (MCD). All diets were similar in composition except for their K+ contents, which were 100, 300, 500, and 700 meq/kg in groups 1-4, respectively. In these adx animals, Na-K-ATPase activity increased greater than 200% in the CCD as the dietary intake of K+ increased. There was a linear relationship between K+ excretion and the enzyme activity in this segment. There was a 50% increase in Na-K-ATPase activity in the CNT as the dietary intake of K+ increased in adx animals. However, there were no significant differences in Na-K-ATPase activities in the DCT and MCD among the four treatment groups. It is concluded that dietary K+ intake can influence Na-K-ATPase activity in the CCD and CNT independently of plasma aldosterone levels.