A scanning electron microscopic study on the fractured rat parietal cells in resting state and after stimulation with tetragastrin.

Parietal cells in the rat gastric mucosa fractured by freeze cracking methods under resting (control) state and tetragastrin stimulation were studied by field emission scanning electron microscopy. The structures thus revealed were compared with those studied by transmission electron microscopy. In the fractured cytoplasm, intracellular canaliculi lined by numerous microvilli invaginated deeply towards the basal cytoplasm. Tubulovesicles appeared as many small holes about 0.05mu in diameter and were distributed predominantly in the apical or pericanalicular cytoplasm. Some tubulovesicles directly opened into the secretory canaliculi. Occasionally, tiny microvilli appeared in tubulovesicles. After being stimulated for 30 min with tetragastrin, the secretory canaliculi of parietal cells became enlarged and there were a concomitant increase in both the number and size of microvilli. Tubulovesicles also were increased in size and number and the tiny microvilli in them were also increased. The tubulovesicles were enlarged presumably as a result of membrane fusion between contiguous tubulovesicles. It was found that the enlargement of the secretory canaliculi was the result of fusion of the membrane of a single tubulovesicle or a confluence of tubulovesicles to that of the secretory canaliculus and the successive disappearance of the fused membrane.