REGULATION OF NA-ATPASE IN THE RAT OUTER MEDULLARY COLLECTING DUCT DURING POTASSIUM-DEPLETION(, K+)

Because in outer medullary collecting ducts (OMCD) of K+-depleted rats , K+ secretion is abolished, whereas Na+, K+- ATPase, which energizes this secretion, is markedly stimulated, it has been proposed that Na+, K+-ATPase was mislocated to the apical cell membrane and energized K reabsorption. This hypothesis has been supported by paradoxical effec ts of ouabain in K+-depleted compared with normal rats. However, we ha ve recently shown that ouabain inhibits not only Na+, K+-ATPase but al so apical H+, K+-ATPase in the OMCD of K+-depleted rats. Therefore, th is study was designed to evaluate whether previous observations were a ccounted for by Na+, K+-ATPase or by ouabain-sensitive H+, K+-ATPase. Na+, K+-ATPase was distinguished from H+, K+-ATPase by its insensitivi ty to Sch-28080. Results indicate that the hydrolytic and transport ac tivities of Na+, K+-ATPase, the number of its functional units, and th e expression of mRNA of its alpha(1) and beta(1) subunits were increas ed threefold or more in the OMCD of rats fed a K+-depleted diet for 2 wk. By immunofluorescence, Na+, K+-ATPase staining was strongly increa sed in K+-depleted rats but remained localized to the basolateral pole of OMCD principal cells. In conclusion, K+ depletion is associated wi th marked induction of functional Na+, K+ pumps at the basolateral pol e of rat OMCD. Therefore, reduced K+ secretion might result from inhib ition of apical K+ conductances and stimulation of basolateral K+ recy cling. It is proposed that increased Na+, K+-ATPase participates in th e increased Na+ reabsorption prevailing in collecting ducts of K+-depl eted rats.