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Biomedical subjects

A Perrelet

Publications and source records attributed to A Perrelet.

At least 55 records · Page 3Linked to original sources
PubMed1982

Circulating somatostatin acts on the islets of Langerhans by way of a somatostatin-poor compartment.

Somatostatin perfused in canine pancreases at 10 to 20 picograms per milliliter or 10 to 20 percent of the pancreatic vein somatostatin concentration inhibited insulin and glucagon secretion. This suggests that the high local concentration of endogenous somatostatin is not in contact with somatostatin receptors of the islets. The integrity of this separation may determine the sensitivity of islet cells to circulating somatostatin.

Animals↗
PubMed1982

Climbing fiber destruction affects dendrite and spine membrane organization in Purkinje cells.

Destruction of climbing fibers, one of the presynaptic inputs to Purkinje cells, was achieved by intraperitoneal injection of 3-acetylpyridine in rats. Freeze-fracture morphology of the Purkinje cell membrane was studied under these conditions. Quantitative analysis reveals a decrease in the number of intramembrane particles (IMP) in the membrane E-face of dendrites and spines of large dendrites, both postsynaptic targets for climbing fibers. The membrane of the perikaryon and of the spines from the spiny branchlets were unaffected by climbing fiber destruction. These results suggest that under the conditions studied, the membrane organization in well-defined areas of the Purkinje cell may be influenced by presynaptic factors.

Animals↗
PubMed1982

Effects of climbing fiber destruction on large dendrite spines of Purkinje cells.

The number and freeze-fracture membrane organization of spines on Purkinje cell dendrites were studied in rats after destruction, by intraperitoneal injection of 3-acetyl-pyridine (3-AP), of the climbing fiber afferents to the cerebellum. The results obtained show that: (1) there is a 1.6 fold increase in the total number of dendritic spines in the 3-AP-treated animals as compared to controls, but no change in the total number of spine synaptic profiles; (2) the spines from main dendrites in both control and 3-AP-treated animals have more than 1,000 IMP/micron 2 of P-face membrane; and, (3) the spines formed on Purkinje cell dendrites in the absence of their presynaptic axons have the same P-face membrane organization (i.e. more than 1,000 IMP/micron 2) as spines normally innervated by afferent climbing fibers. These data suggest that each type of Purkinje cell spine has a specific P-face membrane organization which does not appear to be influenced by presynaptic terminals.

Afferent Pathways↗
PubMed1982

Distribution of cytochemically detectable cholesterol in the electric organ of Torpedo marmorata.

A cytochemical probe for cholesterol, the polyene antibiotic filipin, was applied to aldehyde-fixed samples of the electric organ of Torpedo marmorata to identify filipin-binding sites in the various membrane components of the organ and, hence, the probable cholesterol content at these levels. In both thin-sectioned and freeze-fractured samples, filipin-cholesterol complexes appeared numerous and homogeneously distributed on the Schwann cell plasma membrane. On the presynaptic membrane, filipin-cholesterol complexes occurred in patches alternating with unlabeled membrane segments. The postsynaptic, acetylcholine receptor-rich plasma membrane of the electroplax showed no or few filipin-cholesterol complexes in the flat region and upper part of the invaginations (both areas characterized by a lattice of small intramembrane particles); however, the membrane of the bottom part of the postsynaptic invaginations contained several complexes. The ventral, noninnervated plasma membrane of the electroplax showed a moderate, homogeneous filipin labeling. These data suggest that the distribution of cholesterol among membranes of the electroplax is not homogeneous and that the acetylcholine receptor-rich region of the postsynaptic membrane (as characterized by the lattice of small intramembrane particles) may contain little cholesterol.

Animals↗
PubMed1982

Immunocytochemical localization of the vitamin D-dependent calcium binding protein in chick duodenum.

The vitamin D-dependent calcium binding protein (CaBP) of chick duodenum has been localized by immunocytochemistry and by radioimmunoassay. Light microscopically, CaBP was seen to be present in the absorptive cells of the villi while in other cell types of the villi and the crypts, including goblet cells and endocrine cells, no CaBP was seen. At the electron microscopic level, CaBP was shown to be localized in the cytosol and the euchromatin of the nucleus but not in membrane-bounded cytoplasmic compartments. Quantitative evaluation of the immunocytochemical protein A-gold label showed that the terminal web and the cytosol of basal cellular regions were most highly labeled while the brush border was weakly labeled. The radioimmunoassay evaluation of intestinal subcellular fractions indicated that 96% of the homogenate CaBP is in the cytosol high-speed supernatant fraction. Collectively, these results support the hypothesis that the vitamin D-dependent intestinal CaBP may play a role in either regulation of intracellular calcium concentration or movement of calcium across the brush border membrane from the gut lumen.

Animals↗
PubMed1982

Glicentin precedes glucagon in the developing human pancreas.

A quantitative evaluation of immunofluorescence elicited by anti-insulin, anti-glucagon, anti-glicentin, anti-somatostatin and anti-pancreatic polypeptide antisera has been carried out in the pancreas of 5 human fetuses from 3.0 to 9.6 cm C.R. The data obtained indicate that while insulin and somatostatin-containing cells are approximately in similar proportions with respect to the other endocrine cell types in the five fetuses studied, the glucagon and glicentin immunoreactive cells and the pancreatic polypeptide cells are not : a) pancreatic polypeptide-containing cells increase in proportion as fetuses grow older; b) the youngest fetuses (3.0 to 4.3 cm C.R.) contain a high proportion of cells reacting to anti-glicentin antiserum only (GLI-cells) and a small proportion of cells stained both with the anti-glicentin and anti-glucagon antisera (GLI/GLU-cells). However, the latter cell type which stains similarly as the postnatal and adult pancreatic A-cell (GLI-cells are not detectable in the postnatal and adult pancreas) increases iin proportion in older fetuses, while the proportion of GLI-cells decrease. The data suggest that the definitive adult-type A-cell matures from a GLI-cell type which is not able to convert glucagon precursors GLI(s) into glucagon.

Female↗
PubMed1982

Quantitation of endocrine cell content in the pancreas of nondiabetic and diabetic humans.

The application of immunofluorescence technique with anti-insulin, anti-glucagon, anti-somatostatin, and anti-pancreatic polypeptide (PP) antisera to sections of precisely sampled regions of the human pancreas allowed the quantitative evaluation of the total content of these four endocrine cell populations in 13 nondiabetics, in 2 insulin-dependent diabetics (IDDM), and in 2 non-insulin-dependent diabetic subjects (NIDDM) of various age and sex. In nondiabetic subjects, PP-cells appear sex-related. Male individuals have a significantly greater volume of PP-cells than female. In diabetic subjects, the only marked difference as compared with nondiabetics is the reduction of insulin cell volume in IDDM. Other small differences between individual endocrine cell volumes are detectable in both IDDM and NIDDM as compared with nondiabetics, but their significance is at present unclear. The qualitative changes of islet structure accompanying insulin cell reduction in IDDM were not considered in the present study.

Adolescent↗
PubMed1982

Distribution of intramembrane particles and filipin-sterol complexes in plasma membranes of kidney. I. Corpuscle of Malpighi.

A quantitative study was performed on glomerular cell types from the rat kidney freeze fractured after conventional fixation or following exposure to the sterol-specific antibiotic, filipin. The results reveal a considerable variation on the size and number of intramembrane particles, as well as in the number of filipin-sterol complexes present on plasma membranes of the different cell types present in the glomerulus. These differences in membrane structure probably reflect specialized functions of the individual plasma membranes within the glomerulus. The most striking observation, however, was the low particle content and poor filipin labeling of podocyte foot process bases (which lie against the basal lamina) compared with the rest of the podocyte plasma membrane. The presence of distinct membrane domains in podocytes may be a factor involved in maintaining their specific architecture that is critical for the normal functioning of the kidney filtration barrier.

Animals↗
PubMed1981

Topology of morphologically detectable protein and cholesterol in membranes of polypeptide-secreting cells.

The freeze-fracture morphology of intracellular and plasma membranes in endocrine and exocrine polypeptide-secreting cells has been studied to detect changes while these membranes interact during secretion. A qualitative and quantitative evaluation of intramembrane particles and filipin binding as indicators of protein and cholesterol content of the membranes, respectively, reveals the following changes. From the forming of the maturing pole of the Golgi complex, membranes lose morphologically detectable protein and gain morphologically detectable cholesterol. The protein-poor, cholesterol-rich secretory granule membrane then interacts with a richly particulate plasma membrane in endocrine cells and with a moderately particulate luminal membrane in exocrine cells. The site of interaction between secretory granule and plasma membrane is characterized by a local clearing of intramembrane particles; by contrast, filipin-binding sites revealing cholesterol are present in this area. In exocrine cells, the fused secretory granule, which is initially rich in filipin-cholesterol complexes and poor in particles, appears to lose progressively its filipin labelling to resemble the poorly labelled luminal membrane. These findings, although they cannot be interpreted definitely at present, clearly show impressive changes of membrane structure along the secretory pathway and suggest that a corresponding degree of functional specialization is needed for proper interaction to occur.

Animals↗
PubMed1981

Freeze-fracture of developing neuronal plasma membrane in postnatal cerebellum.

The structure of the plasma membrane of two neuronal cell types was quantitatively assessed in freeze-fracture replicas of rat cerebellar cortex from 2 to 73 postnatal days. The measurement of the number and size of intramembrane particles (IMP) in different regions of the Purkinje cells and of the granule cell showed that between 2 and 21 postnatal days there was a differential increase in the number of IMP; several regions of the cell characterized by a different pattern of synaptic interconnections showed differences in particle size and in particle number: neuronal processes had lower numbers of IMP than perikarya, whereas dendrite spines contained fewer IMP than dendritic trunks. These differences in IMP content appeared at the time at which specific synaptic contacts are established in these various regions of the cells.

Age Factors↗
PubMed1981

Heterogeneous distribution of filipin--cholesterol complexes across the cisternae of the Golgi apparatus.

The Golgi apparatus is a key element in the ordered movement of secretory polypeptides from the rough endoplasmic reticulum to the plasma membrane during secretion. It has been shown that cisternae that receive membranes from the reticulum are morphologically similar to the latter and that cisternae liberating secretory granules resemble that plasma membrane. By using an ultrastructural probe for membrane cholesterol, filipin, on freeze-fractured and thin-sectioned exocrine and endocrine pancreatic cells, we have shown that an enrichment in filipin-cholesterol complexes takes places across the stacked cisternae of the Golgi apparatus; the reticulum-related (forming) cisternae are poor in such complexes, but the secretory granule-related (maturing) cisternae contain numerous complexes. Secretory granule membrane is also richly labeled with filipin-cholesterol complexes. The heterogeneous cholesterol distribution in the membranes of the Golgi apparatus, as shown by filipin, emphasizes the polarity of this organelle, in agreement with its role in organizing the traffic of the secretory polypeptides from the rough endoplasmic reticulum to the plasma membrane.

Animals↗
PubMed1981

Insulin immunoreactive sites demonstrated in the Golgi apparatus of pancreatic B cells.

Insulin immunoreactive sites were localized in the Golgi apparatus of pancreatic B cells by light and electron microscopy. Identification of the Golgi apparatus by immunofluorescence required the prior degranulation of B cells with glibenclamide to reduce the insulin immunostaining due to secretory granules. In such cells, insulin immunofluorescence revealed brightly stained, crescent-shaped strands with form and location super-imposable on that of Golgi complexes seen in thin sections of the same cells. With the electron microscope, the insulin immunoreactive sites revealed by the protein A/gold technique were localized in the cisternae and vesicles of the Golgi apparatus of glibenclamide-treated and control B cells and over maturing and mature secretory granules. The quantitative evaluation of the intensity of the insulin immunoreactive sites in the Golgi apparatus revealed a density of sites 4 times more than cellular background values. The demonstration of insulin immunoreactivity in the Golgi apparatus provides direct evidence for the involvement of this compartment in the transport and maturation of proinsulin into insulin.

Animals↗