Studies on the Depletion and Accumulation of Microvilli and Changes in the Tubulovesicular Compartment of Mouse Parietal Cells in Relation to Gastric Acid Secretion

Abstract

Gastric parietal cells in mice present a spectrum of microscopic appearances due mainly to variations in the abundance of the tubular and vesicular component of the cytoplasm and in the size and number of microvilli lining the intracellular canaliculi. Differences in the range of forms among parietal cells of fasting versus fed mice were not especially striking, but cells with very numerous tubules and vesicles were more common after fasting. However, in mice treated with drugs or hormones that induce acid secretion, parietal cells were more uniform in appearance. There was a marked reduction of these cytoplasmic membranes and a concomitant increase in both the number and size of microvilli. Measurements of acid secretion in control animals and in animals treated with acid secretagogues indicated hydrogen ion secretion contemporaneous with depletion of the cytoplasmic tubulovesicular membranes and with increase of the microvilli. In mice with inhibited acid secretion, parietal cells showed an accumulation of cytoplasmic tubules and vesicles and reduction in the numbers of microvilli. Stereological methods were used to quant~tate 10 different parietal cell compartments. Tracer studies with lanthanum did not reveal continuity between the tubules and the plasma membrane. However, there were regions of close apposition between the tubulovesicular membranes and the cell membrane of the canaliculus, and instances where cytoplasmic tubules extended from the cell into the core of enlarged microvilli.

Selective high-level expression of epsin 3 in gastric parietal cells, where it is localized at endocytic sites of apical canaliculi

“…First, EHD proteins play a role in recycling from the endosome to the plasma membrane (20,21,25), and thus may be implicated in membrane shuttling from tubulovesicles to the plasma membrane of canaliculi. Second, purified EHD proteins can deform lipid bilayers both in vitro (19) and in vivo (26,27) to generate EHD-coated tubules that are in the same size range as tubulovesicles of gastric parietal cells (27,28). Third, they contain an EH domain homologous to the EH domain of the epsin interactor Eps15 (i.e., a domain predicting a potential interaction with the NPF motifs present in the C-terminal region of the epsins) (25, 29, 30).…”

A Scanning Electron Microscopic Study on the Fractured Rat Parietal Cells in Resting State and after Stimulation with Tetragastrin

“…Several authors have attempted to demonstrate the continuity between membranes of the canalicular system and tubulovesicles by TEM observation (SEDAR, 1961;LEESON, 1973), the freeze etch method (LEESON, 1972;ITO and SCHOFIELD, 1974) and tracer methods (ITO and SCHOFIELD, 1974). However, their results are still controversial and by no means conclusive.…”

“…As close appositions of the membrane between secretory canaliculi and tubulovesicles often occurred (ITO and SCHOFIELD, 1974), tubulovesicles are more prominent in resting cells (LEESON, 1973), and canaliculi are extensive after stimulation (LEESON, 1973), the membrane flow between the two during the secretory cycle has been strongly assumed (LEESON, 1973).…”

Changes in Subcellular Structures of Parietal Cells in the Rat Gastric Gland after Omeprazole.

“…Corresponding to acid production and secretion in parietal cells, the membrane flow with the proton pump occurs between tubulovesicles and plasma membrane (ITO and SCHOFIELD, 1974;PILLAY et al, 1977); this occurs by membranous fusion of tubulovesicles with the plasma membrane on acid secretion, while on inhibition of acid secretion, membranes are retrieved from the plasma membrane by pinocytosis. Omeprazole's inhibition of acid secretion has been demonstrated to be due to its binding with H+-K+-ATPase within vesicle membranes (BELL et al, 1988).…”