SAP 97 is a potential candidate for basolateral fixation of ezrin in parietal cells

Acid secretion in gastric parietal cells is preceded by a dramatic increase in surface area of the apical membrane compartment, due to fusion of the H+/K(+)-ATPase-containing tubulovesicles. The resulting canaliculi must be fixed for a period of minutes by cytoskeletal elements to sustain acid secretion. Using immunofluorescence microscopy, the cytoskeletal linker molecule, ezrin, localizes to the apical canalicular membrane of parietal cells. Antibodies against ezrin precipitate H+/K(+)-ATPase and beta-actin. In addition to its apical localization, ezrin is found to be colocalized at the basolateral compartment with synapse-associated protein (SAP) 97. Immunoprecipitation confirms a direct binding of SAP 97 and ezrin. We conclude that ezrin is fixed to the basolateral compartment by SAP 97. Upon stimulation of acid secretion, ezrin moves to the apical surface where it might stabilize the canalicular microvilli by connecting to beta-actin and H+/K(+)-ATPase, thereby sustaining acid secretion.