IDENTIFICATION OF GASTRIC H,K-ATPASE IN AN EARLY VERTEBRATE, THE ATLANTIC STINGRAY DASYATIS-SABINA

Virtually all vertebrates acidify their gastric contents to a pH betwe en 0.8 and 2.0. In mammals, acid secretion is mediated by a K-stimulat ed proton-translocating adenosine triphosphatase (H,K-ATPase), which e stablishes a million-fold gradient of protons across the apical membra ne of the gastric parietal cell. The earliest phylogenetic appearance of gastric acid secretion is in cartilaginous fish, and we sought to v erify in this class (Chondrichthyes) the presence and distribution of H,K-ATPase in gastric epithelial cells. An antibody against a syntheti c peptide based on the C-terminus of pig H,K-ATPase alpha-subunit was localized in the gastric glands of the Atlantic stingray Dasyatis sabi na. The C-terminal antibody stained all cells with tubulovesicles and the apical membrane domain of mucous neck cells. In proximal stomach, gastric glands showed the strongest immunoreactivity in cells close to the isthmus; in the distal stomach, strongest immunoreactivity was fo und in cells at the base of the glands. Oxyntic cells were more intens ely immunoreactive than oxynticopeptic cells. This antibody labeled a single band of M(r) 100,600 on immunoblots of D. sabina gastric micros omes. These results show the earliest phylogenetic occurrence of a gas tric ATPase in putative acid secreting cells and suggest that this enz yme shares structural features with mammalian H,K-ATPase.