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Biomedical subjects

M Amherdt

Publications and source records attributed to M Amherdt.

At least 91 records · Page 5Linked to original sources
PubMed1975

An apparent abnormaltiy of the B-cell microtubular system in spiny mice (Acomys cahirinus).

The pancreatic B-cell contains microtubules, which are thought to participate in the process of insulin release. In order to disclose a possible abnormaltiy of this B-cell microtubular system in animals with islet dysfunction, isolated islets from normal rats and mice, as well as from diabetic mutant mice (DBM mice) and from spiny mice (Acomys cahirinus) were incubated in the presence of vincristine, which causes the precipitation of the microtubular protein into paracrystalline deposits. Ultrastructural examination of the islets indicated that the volume-density of vincristine-induced deposits was markedly reduced in B-cells of spiny mice, when compared to that found in normal rats and mice and DBM mice. Exposure of the islets from spiny mice to a high glucose concentration, concomittantly to vincristine, caused a further reduction in vincristine-induced crystals content of the B-cell. It is speculated that an impairment of the B-cell microtubular system may account for the deficiency of insulin release found in spiny mice.

Animals↗
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

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↗
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↗
PubMed1973

Exocytosis-endocytosis coupling in the pancreatic beta cell.

The stimulation of the release of insulin by glucose is accompanied by an enhanced uptake of cytochemically demonstrable horseradish peroxidase into endocytotic vesicles within the beta cells. An exocytosis-endocytosis coupling might represent a mechanism by which membrane constituents are recycled within the beta cells under conditions of increased secretory activity.

Animals↗
PubMed1973

Pronase effect on pancreatic beta cell secretion and morphology.

Pronase at low concentration (4 micrograms per milliliter) produces a reversible increase of glucose-stimulated insulin release in isolated islets of Langerhans. Pronase also affects the ultrastructure of the beta cells by inducing extensive development of tight junctions as well as the accumulation of secretory product within the extracellular spaces.

Animals↗
PubMed1973

Insulin release by emiocytosis: demonstration with freeze-etching technique.

The technique of freeze-etching for electron microscopy applied to isolated islets of Langerhans has permitted a successful evaluation of emiocytotic events on the cell surface. The frequency of these events in stimulated cells suggests that emiocytosis represents a significant mechanism for insulin release.

Animals↗
PubMed1971

Morphological and biochemical studies of B cells of fetal rat endocrine pancreas in organ culture. Evidence for (pro) insulin biosynthesis.

Fetal rat pancreases explanted on the 18th day of gestation and maintained in organ culture for 1-10 days were utilized for this series of studies. Ultrastructurally, at the time of explantation, the majority of fetal B cells was sparsely granulated and characterized by numerous free ribosomes and undeveloped rough endoplasmic reticulum (RER) and Golgi complexes. During the culture period, extensive development of the RER and Golgi complexes preceded an increasing accumulation of beta-granules. This later increase in the number of beta-granules and in the concentration of immunoreactive insulin was paralleled by a reduction of RER and Golgi complex activity. High resolution radioautographic studies of pulse-chase experiment over a 1 hr period demonstrated the shift of silver grains from the elements of the RER, through the Golgi region, and finally to the beta-granules. Incubation with (14)C-labeled leucine demonstrated the incorporation of radioactivity into molecules possessing the immunological and electrophoretic properties of insulin. These studies indicate that de novo synthesis of (pro)insulin occurs also during culture of fetal rat pancreas explanted relatively late in gestation.

Animals↗