Characterization of gastric mucosal membranes. X. Immunological studies of gastric (H+ + K+)-ATPase.

Abstract

Gastric mucosal homogenates from hog were fractionated by differential and density gradient centrifugation and free-flow electrophoresis. The 2 major membrane fractions (FI and FII) thus obtained are distinct both enzymically and in terms of transport reactivity. This heterogenicity extends to their antigenic activity. Purified antibodies which were raised against the K+-ATPase-containing H+ transport fraction FI were of 2 types: inhibitory and non-inhibitory. Inhibitory antibodies reduced the K+-ATPase activity by .apprx. 80% and the K+-p-nitrophenylphosphatase activity by .apprx. 40% in a concentration-dependent manner, while the small Mg2+-dependent component of the enzyme activity was unaffected. Antibodies inhibiting the K+-ATPase also inhibited H+ transport. These antibodies did not cross-react with the other major membrane fraction isolated by free-flow electrophoresis, FII, and gave a single band on rocket immunoelectrophoresis. Antibodies against this FII fraction also did not react with the K+-ATPase and were heterogeneous, giving at least 4 bands with rocket immunoelectrophoresis and inhibiting both the 5''-nucleotidase and Mg2+-ATPase of this fraction. Immunofluorescent staining of tissue sections showed that the FI was derived from the parietal cells of gastric tissue and was localized to the supranuclear area of the cell. Staining of isolated rat gastric cell suspensions by FI antibodies confirmed the selectivity of the antibody and showed a polar, plasma membrane localization. FII antibodies also largely stained the parietal cells in tissue sections. In the 16 hog tissues tested, FI antibodies cross-reacted only with gastric fundus, thyroid and weakly with thymus. Immunoelectronmicroscopy showed that FI antibodies reacted strongly with the secretory membrane at the apical cell surface of the parietal cells and at the secretory canaliculi, weakly with the apical surface of the zymogen cell, and not with the basal-lateral surface of the cells. The proton-translocating ATPase is localized in the parietal cells and in the region postulated to be the site of acid secretion.