THE EARLY CHANGES OF PARIETAL-CELL STRUCTURE IN THE COURSE OF SECRETORY ACTIVITY IN THE RAT
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1985
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Abstract
The fine structure of the rat parietal cell was studied, at rest and after stimulation by refeeding or insulin administration. Experiments on fixation procedures showed that whenever the fixative contained sucrose at a concentration higher than 0.2 M, the system of cytoplasmic membranes was clearly tubular in arrangement, whereas the omission of sucrose in the fixative usually resulted in a vesicular structure. High-voltage EM of thick sections prepared by conventional techniques or by impregnation with zinc iodide-osmium (ZIO) revealed that the tubules were grouped into fascicles and these formed a feltwork that was especially thick toward the cell apex. The development of the secretory canaliculus after stimulation appeared to take place by an in situ remodeling of the cytoplasmic domain occupied by the tubular system. Cells examined after short periods of stimulation (5-15 min) showed images of the tubular system and of the canalicular structure which differed both from the nonstimulated and from the fully active (30-45 min of stimulation) cell. These features included the formation of wide cisternae and of pericanalicular cytoplasmic trabeculae or laminae, whose fine structure beared close resemblance to the intracanalicular processes in the same cells. These images can be ordered into a hypothetical sequence which may be a model to explain the transformation of the tubular system and intervening cytoplasmic matrix into secretory canaliculus.