Effects of potassium bicarbonate on distal nephron Na-K-ATPase in adrenalectomized rabbits

Na-K-ATPase activity in the connecting tubule (CNT) and cortical collecting duct (CCD) has been shown to be influenced by KCl both in the presence and in the absence of aldosterone. To investigate if the aldosterone-independent effect of K+ on Na-K-ATPase can be produced by other K+ salts, we studied the effects of dietary KHCO3 on Na-K-ATPase and ouabain-insensitive Mg-ATPase activities in four nephron segments of adrenalectomized (ADX) rabbits. The segments examined were: the distal convoluted tubule (DCT), CNT, CCD and medullary collecting duct (MCD). All diets were similar in composition except their KHCO3 contents which were 100, 300, 500 and 700 meq/kg in groups 1 to 4 respectively. Increasing KHCO3 in the diet increased K+ excretion (7 X) and urine pH (6.6 to 8.3). Na-K-ATPase activity in the CCD increased greater than 200% as dietary KHCO3 was increased to 700 meq/kg. There was a linear relation between Na-K-ATPase activity in this segment and steady state plasma K+ as well as K+ excretion in the urine. However, Na-K-ATPase activity in the CCD was lower in KHCO3-fed ADX rabbits than the KCl-fed animals studied previously under similar conditions. There were no significant differences in Na-K-ATPase activities in DCT, CNT and MCD among the four groups given different KHCO3-diets. It is concluded that dietary intake of KHCO3 can also influence Na-K-ATPase activity in the CCD independent of aldosterone.