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R Pochet

Publications and source records attributed to R Pochet.

At least 55 records · Page 3Linked to original sources
PubMed1991

Heterogeneous changes in [Ca2+]i induced by glucose, tolbutamide and K+ in single rat pancreatic B cells.

The effects of glucose, tolbutamide and K+ on cytosolic free Ca2+ ([Ca2+]i) in single rat pancreatic B cells were examined using Fura-2 and dual wavelength microfluorimetry. At basal glucose concentration (2.8 mM), about half of the cells were found to display spontaneous Ca2+ oscillations. Glucose (greater than or equal to 11.1 mM), tolbutamide (greater than or equal to 50 microM) and K+ (50 mM) induced rises in [Ca2+]i that could be inhibited by the Ca2+ channel blocker D600. The pattern of response and the sensitivity to the secretagogues were characterized by a marked heterogeneity. The majority of the cells responded to glucose and tolbutamide by a progressive increase in [Ca2+]i onto which sinusoidal oscillations were superimposed. The periodicity of these oscillations was about 2.5/min. Occasionally, some cells displayed slow and major waves in Ca2+ levels (about 0.2/min). None of the cells responded to glucose by displaying an initial decrease in [Ca2+]i. Likewise, the sugar failed to decrease [Ca2+]i in the absence of extracellular Ca2+. The present study shows that, despite a large heterogeneity of the response, the majority of the pancreatic B cells respond to different secretagogues by displaying fast [Ca2+]i oscillations that are reminiscent of the bursts of electrical activity recorded in B cells.

Animals↗
PubMed1990

Calmodulin and calbindin in pancreatic islet cells.

The process of insulin release evoked by D-glucose and other nutrient secretagogues is triggered by an increase in cytosolic Ca2+ activity. However, some other insulinotropic agents may stimulate insulin release at a close-to-basal concentration of cytosolic ionized calcium. The control of cytosolic Ca2+ concentration depends not solely on the rate of Ca2+ entry into the cell through voltage-sensitive channels and Ca2+ exit via Na(+)-Ca2+ countertransport or active Ca2+ pumping, but also on the subcellular distribution of Ca2+, as dependent, for instance, on both Ca2(+)-ATPase activity and inositol 1,4,5-triphosphate-sensitive release in microsomes and calcium accumulation in mitochondria. Calmodulin and calbindin were both identified in pancreatic islet cells. Activation of adenylate cyclase by calcium-calmodulin may account for the increased production of cyclic AMP in islets stimulated by nutrient secretagogues. Calbindin is present in both normal and tumoral islet cells, and might participate to the alteration of islet function encountered in vitamin D-deprived or repleted rats. However, no target enzyme for calbindin was yet identified in islet cells. Independently of the role of calcium-binding regulatory proteins, the mitochondrial accumulation of calcium may account in part at least, for the preferential stimulation of mitochondrial oxidative events in the process of nutrient-stimulated insulin release.

Animals↗
PubMed1990

Calbindin D28k in mammalian intestinal absorptive cells: immunohistochemical evidence.

Calbindin D28k and D9k are two cytosolic calcium-binding proteins abundant in intestinal absorptive cells which appear to play a role in calcium translocation. Until today, calbindin D28k was found in avian and reptilian absorptive cells but not in mammalian ones. We have described the presence of calbindin D28k-immunoreactivity in intestinal absorptive cells of pig and jerboa (Jaculus jaculus). Pig calbindin D28k-immunoreactive absorptive cells were prominent in duodenum, they were scattered along the villi and nearly absent in the crypts. Jerboa labelled absorptive cells were located along the colonic mucosal surface. No calbindin D28k could be detected in mouse, rat and goat absorptive cells. Topography of calbindin D28k absorptive cells was compared with calbindin D9k distribution. Our results confirmed the data of the literature showing a gradient of labelling increasing from the crypt to the top of the villus and no positive endocrine cell. Young (48 h old) pigs did not expressed calbindin D28k in absorptive cells although calbindin D9k was detected. Calbindin D28K was also observed in endocrine cells which were numerous in pig and goat duodenum and very rare in mouse and jerboa. Western blot experiments confirmed the presence of calbindin D28k in the adult pig intestine, in the jerboa colon and the absence of cross-reactivity between calbindin D28k antibody and calbindin D9k.

Animals↗
PubMed1990

Calbindin and calretinin localization in retina from different species.

Calbindin-D28K and calretinin are homologous calcium-binding proteins localized in many neurons of the central nervous systems. We have compared polyclonal antibodies against calbindin and calretinin and have shown by western blots using purified calbindin and calretinin from rat that (1) anti-calretinin does not recognize calbindin and (2) anti-calbindin presents some cross-reactivity with calretinin. In this report, we have compared by immunohistochemistry the localization of both calcium-binding proteins in the retina of monkey, pig, sheep, rat, cat, pigeon, and salamander. These results are compared with previous data for chick. There are many differences between species and not within species, but some aspects of the distribution are conserved. All species, except rat and monkey, have some cones which contain calbindin only. Most species also have some bipolar cells containing calbindin only. Calretinin is rarely seen in photoreceptors or bipolar cells. All species have horizontal cells which contain calretinin or calbindin or both. All species have amacrine cells and ganglion cells containing one or other protein. In the cat ganglion cell layer, the calretinin antisera define a new, asymmetric, type of cell.

Animals↗
PubMed1989

Calbindin D-28K and parvalbumin immunoreactivity is confined to two separate neuronal subpopulations in the cat visual cortex, whereas partial coexistence is shown in the dorsal lateral geniculate nucleus.

Calbindin D-28K-immunoreactive cells were localized in the supragranular layers of the striate cortex of the cat, while parvalbumin-stained cells occurred from the bottom half of layer II through layer VI, making the two distributions almost complementary. Calbindin- and parvalbumin-positive cells occurred throughout the 3 layers of the dorsal lateral geniculate nucleus (dLGN), but calbindin-immunoreactive cells outnumbered parvalbumin-positive cells. Double labeling on single sections was performed in order to determine the possible coexistence of calbindin and parvalbumin in single cells of cat visual cortex and dLGN. Calbindin and parvalbumin immunoreactivity was found in two separate neuronal populations in the visual cortex, while in the dLGN about 50% of the cells were doubly stained.

Animals↗
PubMed1989

Calbindin-D28 in mammalian brain, retina, and endocrine pancreas: immunohistochemical comparison with calretinin.

Calbindin 28K and calretinin are very similar calcium binding proteins which are both present in the central nervous system (CNS). They respectively bind 4 and 5 Ca++ ions. We have compared by immunohistochemistry and in situ hybridization their localisation in the brain and the retina. The two proteins are generally expressed in different neurons with a few neurons containing both calcium binding proteins. Calbindin 28K is also present in the endocrine system. We have examined the cellular distribution of calbindin in the pancreatic endocrine cells of chick, rat and human and found variable distribution among the different endocrine cell types. We also describe the presence of calbindin in RINm5F cells, an insulin-producing tumor cell line derived from a radiation-induced rat insulinoma.

Animals↗
PubMed1989

Discovery of atrial natriuretic factor in the brain: its characterization and cardiovascular implication.

1. We have devised a radioimmunoassay for atrial natriueretic factor (ANF). Its application to rat brain extract led to the discovery of ANF in the brain. In addition to the hypothalamus and the pontine medullary region, it was widely distributed. 2. ANF in the brain is stored in a low molecular weight form, in contrast to pro-ANF in the atria. Thus, the processing of pro-ANF in the bran neuronal cells is different from that in the atria. 3. ANF was found in the anterior and posterior lobes of the pituitary, the peripheral ganglia, adrenergic neurons, and the adrenal medulla. 4. Brain ANF suppressed stimulated dipsogenesis, basal and stimulated vasopressin release, and angiotensin II-stimulated pressor effects. 5. ANF in the peripheral neuronal system inhibits catecholamine synthesis and release. Thus, central ANF functions to reduce the peripheral fluid volume and vascular tone in concert with the peripheral ANF.

Animals↗
PubMed1989

Presence of calbindin-D 28K in endocrine pancreatic tumoral cells of the RINm5F line.

Calbindin-D 28K expression in insulin-producing tumoral cells of the RINm5F line was assessed by Western-blot and high pressure liquid chromatography. Western blot analysis demonstrated the presence in RINm5F cell homogenates of a protein recognized by a specific polyclonal antibody against chick calbindin. Proteins with apparent molecular weights (mol wt) of 44, 47, 56, and 85 kD were also recognized by the antiserum in RINm5F cell extract, but not in normal rat islet extract. HPLC heat-resistant protein extract from RINm5F cell homogenates revealed three calbindin positive peaks: a major peak with a retention time (20.5 min) identical to that found in a rat cerebellar extract and two minor peaks with shorter retention times. The calbindin content of RINm5F cells was apparently unaffected after 9 d culture in a medium supplemented with 10% calf serum pretreated with dextran-charcoal to remove 1,25-dihydroxyvitamin D3.

Adenoma, Islet Cell↗
PubMed1989

Immunohistochemical localization of GABA-containing neurons during postnatal development of the rat retina.

The localization of neurons containing gamma-amino-butyric acid (GABA)-immunoreactivity has been studied in the rat retina during postnatal development. Two populations of GABA-positive cells were observed. The first was located in the inner layers of the retina, with the number of cells and their immunoreactivity increasing during development until adulthood. Previous studies in adult rat enabled identification of these cells as a subpopulation of amacrine cells. The second was located in the outer layers of the retina. These cells displayed a transient GABA labelling, with no immunoreactivity detectable after postnatal day 15. Their localization and morphology corresponded to calbindin D-27kDa-positive horizontal cells. It was concluded that the transient GABA-positive cells were horizontal cells.

Animals↗
PubMed1988

Pineal-retinal molecular relationships; immunocytochemical evidence of calbindin-27 kDa in pineal transducers.

Calbindin-27 kDa immunocytochemical localization was studied concurrently in the pineal organ and retina from human as well as representatives of all vertebrate classes. Calbindin immunoreactivity was demonstrated in retinal cones (but not in rods) and in pineal transducers (cone-like and modified photoreceptor cells, pinealocytes) of a majority of amniotes. In contrast, no labelling was observed in anamniotes, except in retinal cones of the toad. Labelling was distributed through all cellular compartments (outer and inner segments, perikarya, pedicles or processes) of pineal transducers and retinal cones. Intra- and interspecific variations of calbindin contents are discussed.

Animals↗
PubMed1988

Epithelial and neuronal calbindin in avian intestine. An immunohistochemical study.

It is well known that calbindin immunoreactivity is highly concentrated in the duodenal absorptive cells of young birds. We have shown that in the adult intestine of three avian species, calbindin content is much more variable. In addition to absorptive cells, we have detected throughout the gut of both sexes of the domestic fowl and in the large intestine of the Japanese quail a second type of calbindin-positive epithelial cell which has the shape of a typical endocrine cell. These cells were particularly abundant in the large intestine, in contrast to the usual distribution of endocrine cells along the gut. Calbindin was also detected in the nervous system of the intestine. Calbindin-positive nerve fibres were rare in the duodenum and ileum, numerous in plexuses and nerve processes in both muscular layers and lamina propria of the large intestine in domestic fowl and Japanese quail. In the mallard, nerve fibres were rarely calbindin positive while definitively positive for VIP. Calbindin of the peripheral nervous system of the domestic fowl and Japanese quail comigrates with the duodenal calbindin (27,000 dalton) in SDS gel electrophoresis.

Animals↗
PubMed1988

Calbindin-D28K and the peptidergic neuroendocrine system in rat gut: an immunohistochemical study.

Calbindin-D28K was immunohistochemically localized in myenteric and submucosal plexuses throughout the rat intestine. Calbindin-D28K immunoreactivity was found in about half of myenteric neurons and in more than 90% of submucosal neurons. Calbindin-D28K was also observed in nerve processes running inside ganglia, muscle layers and lamina propria. No correlation could be established between the presence of calbindin-D28K and the distribution of neuropeptides localized in this study (VIP, enkephalin, somatostatin and substance P). In addition, some endocrine-like cells of the ileum were calbindin-D28K-positive. Half of these endocrine cells also contained neurotensin but none of the other neuropeptides investigated.

Animals↗
PubMed1987

Immunohistochemical cross-reactivity and electrophoretic comigration between calbindin D-27 kDa and visinin.

Calbindin D-27 kDa (previously named vitamin D-CaBP or cholecalcin) and visinin present similitude both for their purification procedure and histochemical localization. We systematically compared by histochemistry calbindin and visinin immunoreactive structures in chick and pigeon retina, in rat cerebellum and kidney and in pigeon cerebellum. The calbindin and visinin immunoreactive structures were identical except in the retina. Preabsorption of anti-visinin with purified chick or rat calbindin suppresses the labelling in every organ studied except in the photoreceptor layer of pigeon and chick retina. Such a persistence of labelling was explained by Western blotting analysis of chick-retina soluble proteins showing a pattern of 7 different proteins recognized by anti-visinin even though only one protein was recognized in rat kidney and cerebellum. Anti-visinin is thus a polyclonal antibody reacting with more than one antigen of the chick retina, one of those antigens being calbindin. Calbindin is the single antigen recognized by anti-visinin in the other tested organs. In conclusion, we present evidence that visinin is a calbindin.

Animals↗
PubMed1987

Calbindin in vertebrate classes: immunohistochemical localization and Western blot analysis.

Calbindin immunoreactivity was investigated in various vertebrates. Positive labeling was observed in the absorptive cells of the duodenum of all birds and reptiles but not in mammals, amphibia, or fish. Staining was present in the kidney distal convoluted tubule from amphibia and higher vertebrates. Fish kidney was negative. In the central nervous system of all species investigated, cellular bodies and fibers were Calbindin positive. Their distribution was quite broad and correlates well with the previously reported mapping for chick and rat. Western blot analysis revealed two Calbindins in brain from mammals, birds, reptiles, and amphibia (27,000 and 29,000 Da). Only one band was detected in fish. We conclude that Calbindin from the evolutionary point of view is primarily a neuronal protein, with a highly conservative character.

Amphibians↗
PubMed1987

Calbindin D-27 kDa: preferential localization in non-B islet cells of the rat pancreas.

The presence and abundance of calbindin in rat pancreatic islet cells was assessed by immunohistochemistry of either whole islets or purified B and non-B islet cells, as well as by Western blotting of extracts derived from whole islets and purified B and non-B islet cells. Immunohistochemistry of pancreatic sections indicated a higher calbindin content in non-B cells, located at the periphery of the islets, than in the centrally located insulin-producing B cells. Comparable results were obtained in purified islet cells. Likewise, scanning densitometry of the Western blots indicated that, relative to cell volume, the single calbindin band (Mr 27 kDa) was 5-7 times higher in non-B than in B cells. In the splenic lobe of chick pancreas, however, the opposite situation prevailed. Thus, insulin-producing cells clustered in small roundish islets were more intensely labelled after exposure to anti-calbindin serum than non-B islet cells located in large and irregularly shaped islets. Nevertheless, even in the chick pancreas, non-B islet cells contained an appreciable amount of calbindin.

Animals↗
PubMed1987

Calcium binding protein immunoreactivity in pigeon retina.

Pigeon retina has been mapped immunocytochemically for vitamin D-dependent calcium-binding protein (D-CaBP). Immunoreactivity was found in the cones of the yellow field, but not in photoreceptors of the red field. The D-CaBP-containing cones were a subpopulation of those in the yellow field having straight fibres leading to their synaptic terminals. D-CaBP immunoreactivity was also found in horizontal cells, the amount present varying according to position along the retina, and in some amacrine cells. Immunoblots of pigeon retinal proteins separated by SDS-polyacrylamide gel electrophoresis indicated two D-CaBP forms, having apparent molecular weights of 27000 and 29000. Both these forms of D-CaBP have been found previously in rat and pigeon brain.

Animals↗
PubMed1986

Ultrastructural localization of brain 'vitamin D-dependent' calcium binding proteins.

Rat brain vitamin D-dependent calcium-binding protein (D-CaBP) was assessed for vitamin D dependency, calcium binding and ultrastructural localization within neurons. No evidence of vitamin D dependency could be derived from the experiments on vitamin D-deficient rats. A 95% pure extract of the 27-kDa brain D-CaBP was shown to bind 45Ca on nitrocellulose membrane after sodium dodecyl sulphate-electrophoresis, specifically on the 27-kDa CaBP band. Immunogold staining with electron microscopy allowed detection of D-CaBP into Purkinje cells and climbing fibers of the cerebellum. The immunoreactivity was found to be hyaloplasmic and never membrane-bound. It was present in neuronal soma, neurites and postsynaptic as well as presynaptic terminals. These findings rule out D-CaBP as a possible neurotransmitter and bring further support to the hypothesis that the protein functions as a cytosolic calcium buffer. Immunohistochemical detection of D-CaBP is proposed as a means for morphologic detection of neurons with high calcium metabolism.

Animals↗