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Biomedical subjects

L Orci

Publications and source records attributed to L Orci.

At least 469 records · Page 26Linked to original sources
PubMed1975

Cell contacts in human islets of Langerhans.

The freeze-fracturing technique was applied to fresh human islets of Langerhans. With this technique, the inside of cellular membranes was revealed, and specific membrane differentiations, hitherto unknown, were observed in the plasma membrane of the endocrine cells. The specific membrane differentiations represent two types of intercellular junctions, namely the tight junction, which determines a closure of the extracellular space and the gap junction which allows molecules and ions to diffuse from one cell to another (sharing the gap junction) without leaking in the extracellular space (intercellular coupling). The presence of such junctions may be important for the secretory behavior of the cells within the islet.

Adult↗
PubMed1975

Dynamics of insulin release and microtubular-microfilamentous system. VII. Do microfilaments provide the motive force for the translocation and extrusion of beta granules?

The active role played by beta-cell microfilamentous structures in the dynamics of insulin secretion was investigated by examining the influence of cytochalasin B upon various parameters of hormonal release by the isolated perfused rat pancreas. The view that the cytochalasin-induced changes in insulin release are due to a primary biophysical effect on microfilaments, rather than to an unrelated biochemical alteration of the beta-cell glucose-sensor device, was strengthened by the following observations: (1) the onset and disappearance of the cytochalasin B-induced facilitating action upon insulin release followed a time-course parallel to that characterizing the ultrastructural changes provoked by the drug in the distribution of beta-cell microfilamentous material; and (2) cytochalasin B facilitated leucine-induced insulin release in the presence of a very low glucose concentration. The mold metabolite was also found to transform transient secretory responses into biphasic ones and to prevent the reduction that normally affects the early response to insulinotropic agents when the pancreas is stimulated a few minutes after a prior and short exposure to glucose. The release of insulin evoked by either glucose or gliclazide was abolished in the absence of extracellular calcium, whether in the presence or absence of cytochalasin B. Theophylline and cytochalasin B exerted a synergistic effect upon glucose-induced insulin release. These data support the concept that calcium-dependent contractile events involving cytochalasin B-sensitive microfilamentous structures provide the motive force for both the intracellular translocation and exocytotic release of beta granules.

Animals↗
PubMed1975

Intercellular junctions in podocytes of the nephrotic glomerulus as seen with freeze-fracture.

The glomeruli of rats rendered nephrotic by administration of aminonucleoside of puromycin were studied with the freeze-fracture technique. The alterations of the podocytes consisted of a progressive blunting of the foot processes and of the disappearance of the extracellular space normally present between the foot processes at the level of the slit pore. In parallel with the closure of the extracellular space, fracture faces of the plasma membrane of the latered podocytes revealed the presence of peculiar membrane differentiations represented mainly by irregular chains of membrane-associated particles in the fracture face A and by variegated grooves in the fracture face B. The presence of grooves in fracture face B indicates that the chains of particles in fracture face A are likely to be tight junctions rather than linear gap junctions. However, since the presence of continuous ridges is exceptional, it is suggested that the tight junctions are the "leaky" -type and that the podocytes many have only limited capacities for assembling junctions of the "tight" -type.

Animals↗
PubMed1975

Freeze-fracture differences between plasma membranes of descending and ascending branches of the rat Henle's thin loop.

Freeze-fracture of Henle's thin loop of the rat shows that the plasma membrane of epithelial cells in the descending branch has far more particles (approximately 4000 per sq. mum.) than the plasma membrane in the ascending branch (approximately 1000 per sq. mum). On the contrary, the tight junctions between epithelial cells in the two branches are equally developed. The large number of particles in the descending branch may be an important factor in the water permeability of this tubular segment.

Animals↗
PubMed1974

A peculiar substructure in the postsynaptic membrane of Torpedo electroplax.

Freeze-etching of Torpedo marmorata electroplax reveals an unusual substructure in one of the fracture faces of the postsynaptic membrane. This substructure consists of a lattice of closely spaced particles that are smaller than the usual 80- to 90-A particles present in other membrane types. The lattice occurs exclusively on the B-face of the postsynaptic membrane.

Animals↗
PubMed1974

Hepatic autography in uncontrolled experimental diabetes and its relationships to insulin and glucagon.

Exogenous glucagon is known to increase hepatic lysosomes, but the relationships between endogenous glucagon and insulin levels and hepatic lysosomes have not been examined. To determine if the hormones of the pancreatic islets influence the development of these organelles glycogenosomes, dense bodies, and autophagosomes were morphometrically quantitated in normal rats, in rats with mild streptozotocin diabetes with normal hormone levels, and in rats with severe streptozotocin diabetes with hyperglucagonemia, hypo-insulinemia, and clinical evidence of uncontrolled diabetes and ketoacidosis. In the latter volume density of lysosomes averaged 222.8x10(-4) (SEM +/-19.8x10(-4)), significantly above the control value of 75x10(-4) (SEM +/-7.0x10(-4)) (P<0.0005); glycogenosomes were absent in the diabetics, the increase being largely the result of increased autophagosomes. Insulin treatment corrected the hyperglucagonemia, hypoinsulinemia, and other manifestations of uncontrolled diabetes and reduced the volume density of lysosomes to 37.4x10(-4) (SEM +/-2.0x10(-4)), significantly below both the untreated diabetic rats and the nondiabetic controls (P<0.0025). In mild streptozotocin diabetes, in which hyperglucagonemia, hypoinsulinemia, and other evidence of uncontrolled diabetes were absent, lysosomes averaged 77.6x10(-4) (SEM +/-5.5x10(-4)), not different from the controls. A statistically significant correlation between all measurements of lysosomal volume density and plasma glucagon was observed (r=0.79; P<0.001). It is concluded that uncontrolled streptozotocin diabetes in rats is accompanied by hepatic autophagy which may be related to the increased plasma glucagon level and/or the decreased insulin and which is corrected by insulin therapy.

Animals↗