Biomedical subjects

F Blachier

Publications and source records attributed to F Blachier.

At least 55 records · Page 3Linked to original sources

PubMed1990

Ketone bodies and islet function: 86Rb handling and metabolic data.

The metabolism of ketone bodies was investigated in rat pancreatic islets incubated in the absence or presence of D-glucose. The generation of 14CO2 from 3-14C-labeled ketone bodies, the interconversion of D-(-)-beta-hydroxybutyrate and acetoacetate (AcAc), the reciprocal effects of ketone bodies and D-glucose on their respective catabolism, and the influence of these exogenous nutrients on the output of 14CO2 from islets preincubated with either L-[U-14C]glutamine or [U-14C]palmitate provided an estimation of the nutrient-induced changes in O2 uptake that was in fair agreement with the observed modifications of islet respiration. There was a close correlation between such changes and the corresponding values for insulin output. Because the stimulation of insulin release by ketone bodies also coincided with a decrease in 86Rb outflow from prelabeled islets, these findings suggest that the insulinotropic action of ketone bodies is causally linked to their catabolism through an increase in ATP generation rate and a subsequent decrease in K+ conductance. A complementary participation of changes in mitochondrial redox state to stimulus-secretion coupling is considered, however, in the light of comparisons between the effects of D-(-)-beta-hydroxybutyrate and AcAc, respectively, on mitochondrial NADH generation, 45Ca net uptake, and D-[6-14C]glucose oxidation.

3-Hydroxybutyric Acid↗

PubMed1990

Stimulus-secretion coupling of arginine-induced insulin release: comparison with histidine-induced insulin release.

L-Histidine, when tested at a 10-mM concentration, caused a rapid and sustained stimulation of insulin release from rat islets exposed to either D-glucose (7.0 or 8.3 mM) or L-leucine (10.0 mM). The stimulation of insulin release could not be ascribed to an increase in oxygen uptake, to the generation of histamine from L-histidine, or to its participation in a transglutaminase-catalyzed reaction. Like other cationic amino acids, however, L-histidine rapidly accumulated in islet cells, increased 86Rb outflow from prelabeled islets perifused in the presence or absence of extracellular Ca2+, and stimulated the entry of Ca2+ into islet cells. Yet, the amount of exogenous L-histidine present in the islet cells with a positively charged side chain was estimated to be below the threshold value required for stimulation of insulin release by fully ionized cationic amino acids, such as L-arginine. Hence, the present findings argue against the view that the insulinotropic action of cationic amino acids is solely attributable to the accumulation of these positively charged molecules inside the islet B cell with subsequent depolarization of the plasma membrane.

Animals↗

PubMed1989

Binding of ouabain to normal and tumoral pancreatic islet cells.

The binding of [3H(G)]ouabain was examined in both rat pancreatic islets and tumoral islet cells (RINm5F line). In the islets, the specific binding was considered too low to allow for extensive investigations, taking into account the limited number of islets readily available. In the RINm5F cells, which bound more ouabain than normal islet cells, the time course for binding, its temperature dependency, its competitive inhibition by K+, the number of binding sites, their affinity, and the turnover of ATP per binding site were all similar to those found in other cell types. An incomplete dissociation of [3H(G)]ouabain by unlabelled glycoside and the stimulation of binding by D-glucose were noticed, both phenomena being possibly attributable, in part at least, to the functional response of the RINm5F cells to D-glucose with resulting activation of exocytosis-endocytosis coupling.

Animals↗

PubMed1989

Stimulus-secretion coupling of arginine-induced insulin release. Metabolism of L-arginine and L-ornithine in pancreatic islets.

Exogenous L-arginine and L-ornithine rapidly accumulate in rat pancreatic islets. L-Arginine is converted to L-ornithine and urea. Endogenous or exogenous L-ornithine generates di- and polyamines, the putrescine turnover being faster than that of spermidine and spermine. However, the major pathway for L-ornithine metabolism consists of its transamination to L-glutamaldehyde and further conversion to L-glutamate. The amines and L-glutamate derived from exogenous L-ornithine are incorporated into islet proteins at the intervention of transglutaminase and cycloheximide-sensitive biosynthetic processes, respectively. These findings suggest the hypothesis that the insulinotropic action of L-arginine and L-ornithine could somehow be related to the metabolism of these cationic amino acids in islet cells.

Animals↗

PubMed1989

Stimulus-secretion coupling of arginine-induced insulin release. Functional response of islets to L-arginine and L-ornithine.

L-Arginine and L-ornithine stimulate insulin release from pancreatic islets exposed to D-glucose. This coincides with an increased outflow of 86Rb and 45Ca from prelabelled islets and an increased net uptake of 45Ca by the islets. In the presence of D-glucose, L-lysine stimulates insulin secretion to the same extent as L-arginine or L-ornithine, but the hormonal release is not further enhanced by combinations of these cationic amino acids. L-Arginine or L-ornithine failed to enhance insulin release evoked by either L-leucine or 2-ketoisocaproate. The inhibitor of ornithine decarboxylase D,L-alpha-difluoromethyl ornithine failed to affect the metabolism and insulinotropic action of D-glucose in pancreatic islets, and only caused a partial inhibition of the secretory response to either L-arginine or L-ornithine. The latter amino acids inhibited modestly but significantly D-glucose utilization and oxidation by pancreatic islets. These and complementary findings suggest that the secretory response to L-arginine and L-ornithine is not attributable to any major change in the overall oxidative catabolism of nutrients, but involves mainly a biophysical component, such as the depolarization of the plasma membrane by these cationic amino acids.

Animals↗

PubMed1989

Stimulus-secretion coupling of arginine-induced insulin release. Insulinotropic action of agmatine.

Agmatine causes a concentration-related (0.1-1.0 mM) stimulation of insulin secretion by rat pancreatic islets exposed to D-glucose (5.6-11.1 mM) but, like L-arginine, fails to affect insulin release either in the absence of glucose or at a high concentration (16.7 mM) of the hexose. Agmatine, which accumulates in islet cells, also stimulates 45Ca net uptake by the islets. The secretory response to agmatine represents a delayed process. It is enhanced by theophylline and suppressed by antimycin A or the absence of extracellular Ca2+. The insulinotropic action of agmatine is compatible with the view that endogenously formed polyamines may play a role in the secretory response of islet cells to L-arginine.

Agmatine↗

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

Effect of a phospho-oligosaccharidic putative insulin messenger on insulin release in rats.

The phospho-oligosaccharide extracted from rat liver and supposed to act as the insulin second messenger inhibits glucose-stimulated insulin release. In the present study, this phospho-oligosaccharide was found not to affect D-[U-14C]glucose oxidation and 45Ca net uptake, but to inhibit insulin release evoked by either D-glucose or 2-ketoisocaproate in isolated rat islets. The relative extent of the latter inhibition was unaffected by either the concentration of D-glucose or the presence of dibutyryl-cyclic AMP, forskolin or glucagon in the incubation medium. At variance with the inhibitory effect of clonidine, that of the phospho-oligosaccharide was resistant to both blockade of alpha 2-adrenergic receptors or pre-treatment with the toxin of Bordetella pertussis. It is speculated, therefore, that such a phospho-oligosaccharide might interfere with a distal event in the insulin secretory sequence.

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

Stimulus-secretion coupling of arginine-induced insulin release: metabolism of L-arginine and L-ornithine in tumoral islet cells.

The metabolism of L-arginine and L-ornithine was examined in tumoral islet cells of the RINm5F line and compared to the situation previously characterized in normal rat islets. The maximal velocity of arginase in cell homogenates, as well as either the production of 14C-urea or the steady-state content of 14C-labelled ornithine in intact cells exposed to L-[U-14C]arginine were about one order of magnitude lower in tumoral than normal islet cells. The activity of ornithine-glutamate transaminase was similar in both cell types, and this coincided with a comparable rate of 14C-labelled L-glutamate generation by intact cells exposed to L-[1-14C]ornithine. Despite a comparable cell content in 14C-labelled ornithine of normal and tumoral cells exposed to exogenous ornithine, the rate of di- and polyamine generation was about one order of magnitude higher in tumoral than normal islet cells, this coinciding with a much higher activity of ornithine decarboxylase in RINm5F cell than islet homogenates.

Adenoma, Islet Cell↗

PubMed1989

Stimulus-secretion coupling of arginine-induced insulin release. Uptake of metabolized and nonmetabolized cationic amino acids by pancreatic islets.

In order to assess the possible role of L-arginine accumulation in islet cells as a determinant of its insulinotropic action, the uptake of L-arginine and other cationic amino acids (L-ornithine, L-homoarginine, D,L-alpha-methylornithine, D,L-alpha-difluoromethylornithine) by rat pancreatic islets was compared to the ionic and secretory responses of the islets to the same amino acids. A tight correlation was found between the net uptake of these amino acids and their capacity to stimulate 86Rb efflux, 45Ca uptake and efflux, and insulin release. In the latter respect, there was little difference between metabolized and nonmetabolized amino acids. Thus, although L-homoarginine and 4-amino-1-guanylpiperidine-4-carboxylic acid failed to act as a substrate for either arginase or amino acid aminotransferase in islet homogenates, they both stimulated 86Rb efflux, 45Ca uptake and efflux, and insulin secretion in intact islets. These findings are compatible with the view that the accumulation of these positively charged amino acids in islet cells represents an essential determinant of their secretory action. Hence, the release of insulin evoked by these amino acids could be due to depolarization of the plasma membrane with subsequent gating of voltage-sensitive Ca2+ channels and/or to some other biophysical effect, as suggested by the persistence of a sizeable secretory response to L-arginine or L-ornithine in islets perifused at a high concentrations of extracellular K+ (50 mM).

Amino Acids↗

PubMed1989

Stimulus-secretion coupling of arginine-induced insulin release: comparison with lysine-induced insulin secretion.

L-Lysine, like-L-arginine, L-ornithine, or L-homoarginine, accumulated in rat pancreatic islets and stimulated 86Rb efflux, 45Ca uptake and efflux, and insulin release in islets exposed to D-glucose (7.0 mM). The effect of L-lysine differed from that of the other cationic amino acids by such features as the absence of a threshold concentration for stimulation of insulin release, a much lesser sensitivity of the secretory response to intracellular acidification, and the stimulation of 86Rb net uptake over 60 min of incubation. This coincided with the fact that even in the absence of another exogenous nutrient, L-lysine was well oxidized, augmented NH4+ production, increased both the ATP content and ATP/ADP ratio, caused a time-related decrease in 86Rb fractional outflow, and provoked either a transient (10 mM L-lysine) or sustained (20 mM L-lysine) stimulation of insulin secretion. It is proposed, therefore, that the functional response of the pancreatic B-cell to L-lysine involves not only a biophysical mechanism similar to that responsible for the insulinotropic action of L-homoarginine, but also a significant, albeit modest, metabolic component, which reflects the capacity of L-lysine to act as a fuel in islet cells.

Animals↗

PubMed1988

Effect of exogenous ATP upon inositol phosphate production, cationic fluxes and insulin release in pancreatic islet cells.

Endogenous ATP is thought to play a key regulatory role in nutrient-stimulated insulin release. The present study deals with the effect of exogenous ATP and its stable analog alpha, beta-methylene ATP upon pancreatic islet function. Both alpha, beta-methylene ATP (5.0 microM to 0.2 mM) and ATP (0.3-3.0 mM) caused a rapid and concentration-related increase in insulin output by rat islets incubated or perfused at an intermediate concentration of D-glucose (8.3 mM). The effect of the ATP analog faded out at both lower and higher D-glucose concentrations. In the presence of 8.3 mM D-glucose, ATP also increased both 86Rb and 45Ca outflow from prelabelled islets. The cationic response to ATP persisted in the absence of extracellular Ca2+ and, hence, was reminiscent of that evoked by cholinergic agents. Like carbamylcholine, ATP caused a dose-related increase in the production of [3H]inositol phosphates from prelabelled islets or tumoral islet cells (RINm5F line). The latter effect was duplicated by alpha, beta-methylene ATP and unaffected by atropine. It is speculated that ATP, liberated together with insulin at the exocytotic site, might participate in a positive feedback control of insulin release.

Adenosine Triphosphate↗

PubMed1988

Crabtree effect in tumoral pancreatic islet cells.

The relationship between glycolysis and respiration was examined in a model of pancreatic B-cell dysfunction, namely in tumoral insulin-producing cells of the RINm5F line. A rise in D-glucose concentration from 2.8 to 16.7 mM increased the utilization of D-[5-3H]glucose and production of [14C]lactate from D-[U-14C]glucose, whereas decreasing the oxidation of either D-[U-14C]glucose or D-[6-14C]glucose. Whereas 2.8 mM D-glucose augmented O2 uptake above basal value, a further rise in D-glucose concentration to 16.7 mM decreased respiration, which remained higher, however, than basal value. Whether at low or high concentration, D-glucose exerted a pronounced sparing action upon the oxidation of endogenous nutrients in cells prelabeled with either L-[U-14C]glutamine or [14C]palmitate and, nevertheless, augmented above basal value the rate of lipogenesis, ATP/ADP content, adenylate charge, and cytosolic NADH/NAD+ and NADPH/NADP+ ratios. The generation of ATP resulting from the catabolism of either exogenous D-glucose or endogenous nutrients was not affected by the rise in hexose concentration from 2.8 to 16.7 mM. Thus, in sharp contrast with the situation found in normal islet cells, a rise in D-glucose concentration, instead of stimulating mitochondrial oxidative events, caused, through a Crabtree effect, inhibition of hexose oxidation and O2 consumption in tumoral islet cells.

Adenine Nucleotides↗

PubMed1988

Arachidonic acid metabolism and casein secretion in lactating rabbit mammary epithelial cells: effects of inhibitors of prostaglandins and leukotrienes synthesis.

The metabolism of arachidonic acid (AA) in fragments of lactating rabbit mammary glands in vitro was studied by considering the distribution of 13-[14C]AA in the cells, and the effects of inhibitors of cyclooxygenase and lipoxygenase pathway on the basal and prolactin (PRL)-stimulated casein secretion. 13-[14C]AA was incorporated in all classes of lipids and PRL increased transiently the percentage of free fatty acid after 1 and 5 min. Ten microM ETYA (5,8,11,14-Eicosatetraynoic acid), a tetrayne analogue of AA inhibited prostaglandins F2 alpha (PGF2 alpha) production but not leukotrienes B4 and C4 (LTB4 and LTC4) production and increased basal casein secretion. 10(-4) M DCHA (Docosahexaenoic acid) a competitive inhibitor of prostaglandin-synthetase inhibited PGF2 alpha production but did not affect basal nor PRL-stimulated casein secretion. Fourteen microM indomethacin inhibited PGF2 alpha and LTC4 production and PRL-stimulated casein secretion. Ten microM NdgA (nordihydroguaiaretic acid) an inhibitor of lipoxygenase pathway, inhibited LTB4 and LTC4 production, increased basal level of casein secretion and inhibited PRL-stimulated casein secretion. Hundred microM caffeic acid, an inhibitor of glutathione-S-transferase (GST), a class of enzymes implied in the transformation of LTA4 into LTC4, had the same effect that NDGA on basal and PRL-stimulated casein secretion. These findings show that inhibitors of AA metabolites alter casein secretion.

5,8,11,14-Eicosatetraynoic Acid↗

PubMed1988

Effects of L-leucine, its 2-keto acid metabolite and its non-metabolized analogue on rat tumoral islet cell function.

L-Leucine and 2-ketoisocaproate stimulated insulin release from perifused rat tumoral islet cells (RINm5F line). The secretory response coincided with an increase in the intracellular ATP/ADP ratio, a stimulation of 45Ca outflow from cells perifused in the presence of extracellular Ca2+, and an increase in 32P efflux from cells prelabelled with radioactive orthophosphate. In contrast to D-glucose, however, L-leucine or 2-ketoisocaproate failed to decrease 86Rb outflow, to inhibit 45Ca outflow from cells perifused in the absence of Ca2+ and to enhance the labelling of inositol-containing phospholipids in cells exposed to myo-[2-3H]inositol. These findings suggest that D-glucose, L-leucine and 2-ketoisocaproate exert dissimilar effects on the subcellular distribution of adenine nucleotides and/or 86Rb. The non-metabolized analogue of L-leucine, 2-aminobicyclo[2.2.1]heptane-2-carboxylic acid (BCH), also caused an initial stimulation of insulin release and 32P efflux, but this was soon followed by a severe and irreversible inhibition of insulin output, associated with a permanent enhancement of 86Rb outflow. The dual ionic and secretory response to BCH is interpreted in the light of its dual effect on the catabolism of endogenous amino and fatty acids, and raises the view that BCH could be used to interfere with the function of insulinoma cells.

Adenine Nucleotides↗

PubMed1987

Interference of a nonmetabolized analogue of L-leucine with lipid metabolism in tumoral pancreatic islet cells.

The nonmetabolized analogue of L-leucine, 2-aminobicyclo[2,2,1]heptane-2-carboxylic acid (BCH), was recently found to inhibit O2 uptake and insulin release from tumoral islet cells of the RINm5F line. BCH inhibited lipogenesis, stimulated lipolysis, and severely decreased the oxidation of endogenous [U-14C]palmitate in prelabelled RINm5F cells. D-Glucose exerted metabolic effects which were sometimes opposite to those caused by BCH and, within limits, protected the islet cells against the inhibitor action of BCH. Since BCH augments NH4+ production and facilitated the catabolism of 14C-labelled amino acids in the prelabelled cells, it is proposed that the unexpected inhibition of O2 uptake by BCH is mainly attributable to a decrease in the oxidation of endogenous fatty acids.

Amino Acids↗

PubMed1987

Phospholipase C activation via a GTP-binding protein in tumoral islet cells stimulated by carbamylcholine.

Carbamylcholine and GTP act synergistically in stimulating the production of [3H]inositol-1-phosphate by digitonized tumoral islet cells (RINm5F line) prelabeled with myo-[2-3H(N)]inositol. The response to these two agents is similar to that evoked by GTP gamma S. These findings suggest that a GTP-binding regulatory protein couples the occupancy of muscarinic receptors to activation of phospholipase C in pancreatic islet cells.

Adenoma, Islet Cell↗