RAB11A REDISTRIBUTES TO APICAL SECRETORY CANALICULUS DURING STIMULATION OF GASTRIC PARIETAL-CELLS

Previous investigations in several systems have demonstrated that Rab3 family members redistribute to soluble fractions on fusion of secreto ry granules with target plasma membranes. Rab proteins are then recycl ed back onto mature secretory vesicles after reinternalization of the membrane. Although this cycle is well established for Rab3, far less i s known about redistribution of other Rab proteins during vesicle fusi on and recycling. In the gastric parietal cell, Rab11a is associated w ith H-K-ATPase-containing tubulovesicles, which fuse with the apical p lasma membrane (secretory canaliculus) in response to agonists such as histamine. We have analyzed distribution of Rab11a and other tubulove sicle proteins in resting and histamine-stimulated rabbit parietal cel ls. Stimulation of isolated gastric glands in the presence of 100 mu M histamine and 100 mu M 3-isobutyl-1-methylxanthine did not cause a si gnificant increase in soluble Rab11a. H-K-ATPase, Rab11a, Rab25, synta xin 3, and SCAMPs increased immunoreactivity in stimulus-associated ve sicles prepared from rabbits treated with histamine compared with thos e from ranitidine-treated animals. The large GTPase dynamin was found in both vesicle preparations, but there was no change in amount of imm unoreactivity. Immunofluorescence staining of resting and histamine-st imulated primary cultures of parietal cells demonstrated redistributio n of H-K-ATPase and Rab11a to F-actin-rich canalicular membranes. Dyna min was present on canalicular membranes in resting and stimulated cel ls. These results indicate that Rab11a does not cycle off the membrane during the process of tubulovesicle fusion with the secretory canalic ulus. Thus Rab11a may remain associated with recycling apical membrane vesicle populations.