Ultrastructural changes during stimulation of amphibian oxyntic cells viewed by scanning and transmission electron microscopy

Abstract

Amphibian oxyntic cells exposed by cryofracture were examined by field emission scanning electron microscopy. Comparisons were made between the structure thus revealed and those seen in thin-sectioned material from the same mucosas examined by transmission electron microscopy. Resting oxyntic cells had apical surfaces which were relatively smooth with some short microvilli. Apical cytoplasm was filled with smooth membrane tubules (so-called vesicotubules). Stimulation with a combination of histamine, dibutyryl cyclic AMP, and isobutylmethylxanthine (a phosphodiesterase inhibitor) led to a dramatic elaboration (i.e., increased membrane surface area) and a decrease in number of vesicotubules in the apical cytoplasm. The surface morphology of the stimulated oxyntic cell was much different from that reported for the mammalian parietal cell. Two types of surface elaboration were observed. Most commonly the surface was formed of flattened microplicae or lingulae. An irregular surface formed by the swelling of enlarged spaces near the apical surface was also observed. These new data have been used to evaluate the models which have been proposed to explain the nature of the transition from resting to stimulated morphology. A new model, which incorporates fusion of intracellular vesicotubules with each other and also with apical membrane, is proposed. The proposed fusion process may cause an increase in membrane area open to the extracellular (luminal)solution within the cell (rather than the eversion of membranes into the gastric lumen). Expansion of spaces between the microplicae may be caused by hydroosmotic pressures developed during active HCI secretion.

Expression of H+,K+-ATPase and Glycopattern Analysis in the Gastric Glands of Rana esculenta

“…In fasting conditions, the cytoplasm of these cells is filled with a conspicuous tubulovesicular membrane system. The apical surface is covered with short microvilli (Logsdon and Machen 1982).…”

The early changes of parietal cell structure in the course of secretory activity in the rat

“…This model bears some analogy to the one proposed by Logsdon and Machen (1982) for the oxyntico-peptic cells of amphibians, which involves the lateral fusion of the tubules with the apical zone of the cell and the consequent formation of cytoplasmic lamellae. It requires the presence of a cytoplasmic matrix which is capable of complex changes in coordination with those of the cytomembranes.…”

Ultra-high-resolution scanning electron microscopy of the continuity of cytoplasmic and luminal membranes in frog oxyntic cells

“…Ultrastructural studies of amphibian oxyntic cell have been reported by numerous investigators including (Vial and Orrego, 1960;Sedar, 1961Sedar, , 1965Sedar, , 1969Lillibridge, 1968;Forte and Forte, 1971;Carlisle et al, 1978;Logsdon and Machen, 1982). There is general agreement that the resting oxyntic cell has only a few short microvilli and the small lumen may be packed with a granular substance.…”

“…In the present study, changes in the cytoplasmic membrane system of the resting frog oxyntic cell leading to membrane rearrangement during early stages of histamine stimulation were examined by the method used for the rat stomach. An earlier report on amphibian oxynticopeptic cells by routine SEM methods (Logsdon and Machen, 1982) shows little detail in the cytoplasm. In our study the membranes were clearly visualized because the cytoplasmic matrix was removed by the aldehyde-osmium-DMSO-osmium (A-ODO) method (Tanaka and Mitsushima, 1984).…”