RAB PROTEINS IN GASTRIC PARIETAL-CELLS - EVIDENCE FOR THE MEMBRANE RECYCLING HYPOTHESIS

The gastric parietal cell secretes large quantities of HCl into the lu men of the gastric gland in response to secretagogues such as histamin e. In the membrane recycling hypothesis, this secretory activity requi res the trafficking of the gastric H+/K+-ATPase to the cell surface fr om intracellular tubulovesicles. The Rab subclass of small GTP-binding proteins is thought to confer specificity to vesicle transport throug hout the secretory pathway, and previous investigations established th at Rab11 is highly expressed in gastric parietal cells. Recent discove ries in intra-Golgi transport and neuronal synaptic vesicle fusion hav e fortuitously converged on an evolutionarily conserved protein comple x involved in vesicle docking and fusion. Recent results indicate that Rab11 is involved in the apical targeting of vesicles in parietal cel ls and other epithelial cells throughout the gastrointestinal tract. I n support of the membrane recycling hypothesis, Rab co-segregates with H+/K+-ATPase in parietal cells. The presence of Rab11 on tubulovesicl es supports a role for this Rab protein in recycling vesicle trafficki ng.