Biomedical subjects
Publications and source records attributed to P Meda.
A simple method that permits the attachment of fully dissociated adult pancreatic islet cells to culture dishes, using osmotically disrupted fibroblasts, is described. Using this system, monolayer cultures consisting of either isolated or clustered adult endocrine islet cells can be readily established in standard culture media.
The development of gap junctions between pancreatic B-cells was quantitatively assessed in freeze-fracture replicas of isolated rat islets under various conditions of insulin secretion. Stimulation of insulin secretion by glucose in vitro and by glibenclamide in vivo raised the number of gap junctions between B-cells; glibenclamide alone caused an increase in the size of individual gap junctions. In addition, gap junctions of control and stimulated B-cells showed a packing of particles different from that observed under experimental conditions causing functional uncoupling. The results suggest that gap junctions (and probably coupling) are involved in the secretory activity of B-cells.
The development of gap junctions between pancreatic B-cells was quantitatively assessed in freeze-fracture replicas of isolated rat islets under different conditions of insulin secretion. The results show that in resting B-cells, gap junctions are small and scarce but that these junctions increase when insulin secretion is stimulated. Both a short (90 min) stimulation by glucose in vitro and a prolonged (2.5 d) stimulation by glibenclamide in vivo raise the number of gap junctions; in addition, the glibenclamide stimulation causes an increase in the size of individual gap junctions. As a consequence, the total area occupied by gap junctions on the B-cell membrane and the ratio of this area to the cell volume were found significantly increased in the latter condition. The slight increase of these values observed after the glucose stimulation did not reach significance. These data indicate a change of gap junctions during the secretory activity of the pancreatic B-cells. The possibility that the coupling of the cells is affected by the treatment is discussed.
Lysosomes and their relationships with surrounding organelles were studied in pancreatic B-cells of normal Wistar rats by electron microscopy and cytochemical localization of acid phosphatase (AcPase) and arylsulphatase. Several forms of lysosomes were distinguished and shown to interact frequently with the secretory granules. Two different digestive processes were recognized. During crinophagy, lysosomes directly fuse with secretory granules while, during autophagy, a cytoplasmic area containing secretory granules and/or other organelles is circumscribed before the enzymatic digestion. In addition, lysosomes may transport arylsulphatase into secretory granules apparently not involved in a destructive process. Such a process could also account, at least in part, for the presence of AcPase in a certain number of mature and immature secretory granules.
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