Characterization of K-ATPase activity in distal nephron: stimulation by potassium depletion

Intercalated cells of the distal segments of the mammalian nephron are able to reabsorb K through an active mechanism, particularly during K depletion. However, the molecular basis of this transport is unknown. Therefore, we attempted to determine whether a K-ATPase similar to K-H-ATPase described in gastric mucosa and colon might be present in segments of the distal nephron and thereby account for active K reabsorption. K-stimulated ATPase activity was detected in microdissected segments of rabbit nephron: its activity was proportional to the density of intercalated cells, since it was highest in the connecting tubule, intermediate in the cortical collecting tubule, lowest in the outer medullary collecting tubule, and was not detectable in all other nephron segments. K-ATPase had a high affinity for K (Km approximately equal to 0.2-0.4 mM), was inhibited by vanadate and omeprazole, and was insensitive to ouabain, indicating that it is different from Na+-K+-ATPase but similar to K-H-ATPase. In the rat kidney, K-ATPase was also detected in the collecting tubule and its activity was markedly increased (+100-200%) following K depletion. This stimulation occurred before morphological alterations and might therefore be a primary event responsible for K conservation during K depletion. In summary, these results demonstrate the presence of a vanadate-sensitive, ouabain-insensitive K-ATPase activity in distal nephron segments of mammalian tubules. It is suggested that K-ATPase activity originates in intercalated cells where it might account, at least in part, for K reabsorption.