A Study of Dynamic Membrane Phenomena During the Gastric Secretory Cycle: Fusion, Retrieval and Recycling of Membranes

The possibility of recycling, fusion and retrieval of membranes during the gastric secretory process was studied in isolated gastric mucosae of the toad Bufo marinus. Incorporation and efflux of 14C-inulin and horseradish peroxidase (HRP) into the tissue as well as transmission and freeze-fracture electron microscopic studies during the secretory cycle were done. HRP and 14C-inulin were incorporated into the tubulovesicular membrane system during the secreting-resting transition. Upon restimulation, markers were released towards the lumen. Marker efflux preceded onset of H+ secretion. Morphological transformations in the oxyntic cell as evidenced from transmission and freeze-fracture electron microscopy preceded acid secretion coinciding with marker efflux. At this time, images that have been associated with membrane fusion were found in the apical membranes of oxyntic cells. The results are consistent with a model where membrane area increases by a fusion mechanism at the expense of the tubulovesicular system. This transformation precedes the onset of H+ secretion. Upon cessation of the stimulus or inhibition, membranes are retrieved and the tubulovesicular system reformed. Retrieved membranes could be then reutilized in the next secretory cycle.