Differential localization of colonic H+-K+-ATPase isoforms in surface and crypt cells

Two distinct colonic H+-K+-adenosinetriphosphatase (H+-K+-ATPase) isoforms can be identified in part on the basis of their sensitivity to ouabain. The colonic H+-K+-ATPase alpha-subunit (HKc alpha) was recently cloned, and its message and protein are present in surface (and the upper 20% of crypt cells in the rat distal colon. These studies were performed to establish the spatial distribution of the ouabain-sensitive and ouabain-insensitive components of both H+-K+-ATPase activity in apical membranes prepared from surface and crypt cells and K+-dependent intracellular pH (pH(i)) recovery from an acid load both in isolated perfused colonic crypts and in surface epithelial cells. Whereas H+-K+-ATPase activity in apical membranes from surface cells was 46% ouabain sensitive, its activity in crypt apical membranes was 96% ouabain sensitive. Similarly, K+-dependent pH(i) recovery in isolated crypts was completely ouabain sensitive, whereas in surface cells K+-dependent pH(i) recovery was insensitive to ouabain. These studies provide compelling evidence that HKc alpha encodes the colonic ouabain-insensitive H+-K+-ATPase and that a colonic ouabain-sensitive H+-K+-ATPase isoform is present in colonic crypts and remains to be cloned and identified.