Respective roles of H-ATPase and H-K-ATPase in ion transport in the kidney.

Two types of proton-translocating ATPases, H-ATPase and H-K-ATPase, are found in the renal tubular cells. H-ATPase is present in both endocytic vesicles and apical membranes in almost all nephron segments. On the other hand, H-K-ATPase is present only in the connecting tubule and collecting duct. There is evidence to suggest that H-ATPase may be involved in H secretion in almost all nephron segments. H-K-ATPase is involved not only in H secretion but also in K absorption in the collecting duct segments. Aldosterone administration and metabolic acidosis stimulate the activity of H-ATPase in all collecting duct segments, whereas hypokalemia has only a limited effect on H-ATPase activity. On the other hand, hypokalemia, as well as metabolic acidosis, stimulates H-K-ATPase activity in the collecting duct segments, whereas aldosterone administration alone plays a minor role in the regulation of this enzyme. The physiological role and regulation of H-ATPase in the proximal tubule has not been established.