[Compartment syndrome after Mb Hirschsprung surgery].
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Adult↗
Biomedical subjects
J Sehlin
Publications and source records attributed to J Sehlin.
Effects of glibenclamide and tetracaine on 86Rb+ fluxes in mouse pancreatic beta-cells.
Potassium transport was measured in beta-cell-rich islets from ob/ob-mice using the K+-analogue 86Rb+. Both tetracaine (0.1 mM) and glibenclamide (0.1 microM) reduced the ouabain-resistant 86Rb+ influx but did not significantly affect the ouabain-sensitive portion (Na+/K+ pump). Tetracaine (0.5 - 1 mM) or glibenclamide (0.2 mM) decreased the 86Rb+ equilibrium content and glibenclamide (1 microM) transiently reduced the 86Rb+ efflux rate but 0.1 mM tetracaine had only a slight effect on this flux rate. The results suggest that a change in ouabain-resistant (passive) K+ fluxes, but not the Na+/K+ pump, is involved in stimulation of insulin secretion by glibenclamide and tetracaine. Both drugs may exert similar effects on the beta-cell plasma membrane.
Animals↗
Effect of tetracaine and glibenclamide on 45Ca2+ handling by isolated pancreatic islets.
The 45Ca2+ uptake in beta-cell-rich ob/ob-islets was measured using the La3+ wash technique. Tetracaine (1 mM) markedly enhanced the 45Ca2+ net uptake (120 min) in the presence of 3 mM glucose, and at 7 and 20 mM glucose there were clear tendencies to dose-dependent increases with 0.1 to 1 mM tetracaine. Glibenclamide 1 microM to 0.2 mM, stimulated the 45Ca2+ net uptake in the presence of 3 mM glucose and 0.1 mM to 0.2 mM glibenclamide potentiated the uptake in the presence of 7 mM glucose. When the drugs were added for only a 10 min incubation period, glibenclamide, 1 microM to 0.2 mM, but not tetracaine (10 microM to 1 mM) increased the short-term uptake of 45Ca2+. After preincubation with either of the drugs, neither tetracaine (10 microM to 1 mM) nor glibenclamide (10 nM to 0.2 mM) had any effect on the short-term 45Ca2+ uptake. In islets incubated with 45Ca2+ and tetracaine and washed without La3+ the apparent net uptake of 45Ca2+ was reduced by 0.5 to 1 mM tetracaine both at 3 and 20 mM glucose. Tetracaine (0.5 mM) stimulated the 45Ca2+ efflux in the presence of 3 mM glucose. The results show that both drugs affected the Ca2+ handling. It is suggested that glibenclamide mainly increases Ca2+ influx by voltage-dependent pathways, whereas tetracaine, at certain concentrations, mobilizes Ca2+ from intracellular stores in the islet cells.
Animals↗
Vitamin D3 stimulates calcium-45 uptake by isolated mouse islets in vitro.
Islets isolated from ob/ob mice which had been fed a vitamin D-deficient diet released significantly less insulin in response to glucose than did vitamin D-replete islets but showed normal net 45Ca2+ uptake. To determine whether vitamin D3 has a direct effect on the pancreatic B cell, islets from ob/ob mice on a normal diet were exposed to vitamin D3 in vitro for 1 week or only 3 h, and then glucose-stimulated 45Ca2+ uptake and insulin release were measured. Exposure to 1 nM or 1 microM vitamin D3 for 1 week stimulated 45Ca2+ uptake in the presence of 3 mM, but not 20 mM glucose, and did not affect insulin release. Exposure to vitamin D3 for 3 h did not significantly increase net 45Ca2+ uptake although there was a tendency to such an effect (P = 0.10). In conclusion, vitamin D-deficiency in vivo suppressed subsequent glucose-stimulated insulin release in vitro and this effect may be due to a direct effect of the sterol (or one of its metabolites) on calcium handling by the B cell.
Animals↗
Interaction of sulfonylurea with the pancreatic B-cell.
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4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗
Effect of glucose on the intracellular pH of pancreatic islet cells.
To characterize the effect of glucose on the intracellular pH (pHi) of pancreatic islet cells, we measured the accumulation of 14C-labelled 5,5-dimethyloxazolidine-2,4-dione ( [14C]DMO) in beta-cell-rich islets from ob/ob mice. D-Glucose (20 mM) stimulated insulin release and enhanced the [14C]DMO equilibrium uptake corresponding to an increase of pHi by about 0.15 unit. The glucose effect on DMO uptake was concentration-dependent, with half-maximal effect at about 4 mM-glucose and maximum effect at about 10 mM-glucose. It was inhibited by 20 mM-mannoheptulose and potentiated by 4 mM-L-5-hydroxytryptophan, but not affected by 2 mM-theophylline. Mannoheptulose is an inhibitor and L-5-hydroxytryptophan and theophylline are potentiators of glucose-stimulated insulin release. The glucose-induced increase in pHi appeared rapidly (7 min) and persisted for at least 30 min and it was observed both in bicarbonate/CO2-buffered and in Hepes [4-(2-hydroxyethyl)-1-piperazine-ethanesulphonic acid]-buffered media. Addition of extracellular bicarbonate buffer lowered the pHi, but did not affect basal insulin release, whereas 5 mM-NH4+ increased pHi and induced a 4-fold increase of basal insulin release. We conclude that, in contrast with previous assumptions, glucose increases intracellular pH in the islet cells. This effect may be coupled to the glucose metabolism and associated with triggering of insulin release.
Animals↗
The acyl-amino-alkyl benzoic acid residue and the sulfonylurea containing residue of glibenclamide affect different aspects of beta-cell function.
HB 699 is a non-sulfonylurea acyl-amino-alkyl benzoic acid derivative, corresponding to a major part of the glibenclamide molecule. Basal insulin release (3 mmol/l glucose) as well as glucose-induced release (10 mmol/l glucose) were stimulated by 25 mumol/l and 200 mumol/l HB 699. HB 699 (200 mumol/l) had no effect on the osmotic swelling induced by hypoosmolarity (180 mosm/l). The results indicate that the glibenclamide-induced insulin release can be resolved in a "high-affinity" component, which correlates with increased osmotic resistance in the beta-cells and a "low-affinity" component not associated with increased osmotic resistance. It is suggested that the latter component may be due to the part of the glibenclamide molecule that corresponds to HB 699.
Animals↗
Effect of glibenclamide on the osmotic resistance of pancreatic beta-cells.
The effect of glibenclamide on the osmotic resistance of beta-cells was measured using isolated beta-cells from ob/ob-mice. The beta-cells were incubated at different osmolarity and the diameters of the approximately spherical beta-cells were measured at 22 degrees C or at 37 degrees C with the aid of a screw micrometer eyepiece fitted to a light microscope. A near linear decrease of beta-cell diameter was found with increasing osmolarity (111-617 mosm/l). Control experiments showed that the membrane stabilizers, imipramine (0.1 mmol/l) or tetracaine (1 mmol/l), strongly reduced the osmotic swelling induced by low osmolarity (180 mosm/l). Glibenclamide (0.001 or 0.2 mmol/l) did not affect the beta-cell diameter at normal osmolarity (317 mosm/l) but reduced the swelling induced by hypoosmolarity (180 mosm/l) and the shrinking induced by hyperosmolarity (617 mosm/l). It is suggested that glibenclamide increases the osmotic resistance of isolated beta-cells by changing transmembrane flow of ions.
Animals↗
Different effects of glibenclamide and the structural analogue HB 699 on the 45Ca2+ uptake by ob/ob-mouse islets.
The effects on 45Ca2+ uptake of HB 699, an acyl-amino-alkyl benzoic acid derivative, was compared to those of glibenclamide in incubations using the La3+ wash technique. HB 699 enhanced the 45Ca2+ net uptake in a concentration range (10-200 microM) where insulin release was also stimulated. Glibenclamide showed maximum stimulation of 45Ca2+ net uptake already at 1 microM. HB 699 did not clearly stimulate the short-term 45Ca2+ uptake whether or not the islets were preincubated with the drug. It is suggested that HB 699-induced insulin release is mediated, at least partly, by increased mobility of beta-cell Ca2+.
Animals↗
Effects of 5-hydroxytryptamine on rubidium ion fluxes and insulin release in cultured pancreatic islets.
We have incubated pancreatic islets isolated from noninbred ob/ob mice and NMRI mice for 3 days with or without 5-hydroxytryptamine (5-HT) in the medium and tested the effect of such long term treatment on subsequent insulin release and 86Rb+ accumulation and efflux. Two tenths millimolars of 5-HT abolished insulin release in response to 20 mM glucose. Two tenths millimolars of 5-HT also diminished the ability of islets to accumulate 86Rb+ and the effect of 10 mM glucose on 86Rb+ efflux. One one-hundredth millimolars of 5-HT had no effect on insulin release or 86Rb+ fluxes. Clearly, islets subjected to 5-HT for 3 days at concentrations that do not elicit demonstrable effects in short term incubations show a reduced secretory response. However, the physiological role of the high affinity uptake system for 5-HT in islet cells [Michaelis-Menten constant (Km) = 1.6 microM] remains unknown.
Animals↗
Glibenclamide is exceptional among hypoglycaemic sulphonylureas in accumulating progressively in beta-cell-rich pancreatic islets.
Six hypoglycaemic sulphonylurea compounds were compared with regard to their ability to bind to beta-cell-rich pancreatic islets microdissected from ob/ob-mice. Glibenclamide differed from carbutamide, tolbutamide, chlorpropamide, glibornuride and glipizide in not being rapidly bound to an equilibrium, but accumulating progressively in amounts far exceeding the water space. An inhibitor of the anion channels in the beta-cell membrane, 4-acetamido-4'-isothiocyanate-stilbene-2,2'-disulphonic acid (SITS), suppressed the islet uptake of glibenclamide and to some extent also that of carbutamide and glibornuride. The unusual uptake characteristics of glibenclamide had their counterpart in a retardation of its maximal action in promoting the entry of Ca2+ into the beta-cells.
Animals↗
Phosphate flush and glucose metabolism in pancreatic islets of young and old diabetic mice (C57BL/KsJ-db/db).
Pancreatic islets from normal C57BL/KsJ-+/+-mice and diabetic C57BL/KsJ-db/db-mice were collagenase-isolated and incubated with 33P-labelled inorganic phosphate. No significant difference was observed in phosphate uptake between normal and diabetic mouse islets whether the animals were young (6-8 weeks) or old (27 +/- 9 weeks). When 33P-labelled islets were perifused with non-radioactive medium, all types of islets exhibited a brisk and transient peak of phosphate release in response to a change of glucose concentration from 2.8 to 16.7 mmol/l. Expressed in absolute terms, both the basal and peak efflux of phosphate appeared to be diminished in the diabetic mice. In relative terms (peak over basal), the glucose-stimulated phosphate efflux was not lower in diabetic than in normal mice. At both a low (3 mmol/l) and a high (20 mmol/l) glucose concentration, the production of 3H2O from D-[5-3H]glucose was reduced in old but not in young diabetic mouse islets. The percentage increase in glucose metabolism in response to a rise in glucose concentration from 3 to 20 mmol/l was about the same in all types of islets. The results add to previous observations of disturbed ionic fluxes in the pancreatic islets of diabetic KsJ-db/db-mice. These effects are probably not due to gross alterations in glycolytic metabolism but more probably reflect alterations in the function of the beta-cell plasma membrane.
Age Factors↗
Effect of tetracaine and lidocaine on insulin release in isolated mouse pancreatic islets.
The effect of tetracaine and lidocaine on insulin secretion and glucose oxidation by islets of ob/ob-mice was measured. Tetracaine, at a concentration of 1 microM to 0.1 mM, did not markedly influence the basal (3 mM glucose) insulin secretion, whereas 0.5-3.5 mM induced a marked increase. At 7 mM glucose, there was a dose-dependent increase with 0.1-2.5 mM tetracaine. Insulin release induced by 20 mM glucose was potentiated by 0.1 mM and 0.5 mM tetracaine, but this effect disappeared at 1 mM tetracaine. The stimulatory effect of 0.5-1 mM tetracaine on basal insulin release was blocked by the secretory inhibitors, adrenaline (1 microM), clonidine (1 microM) and by Ca2+-deficiency, but the stimulation by 3.5 mM tetracaine was not reduced by 1 microM clonidine or Ca2+ deficiency. Atropine (10 microM) did not affect the stimulation by 0.5 mM tetracaine at 3 mM glucose or by 0.25 mM tetracaine at 20 mM glucose. Tetracaine, at 0.1 mM, potentiated the secretory stimulation of 20 mM L-leucine, 20 mM D-mannose, or 1 microM glibenclamide. Mannoheptulose, 10 mM, abolished the combined effects of 0.1 mM tetracaine and 10 mM glucose. Lidocaine, 1-5 mM, stimulated basal insulin release, but 1 microM-1 mM of the drug did not affect glucose-induced (20 mM glucose) insulin release and 5 mM lidocaine inhibited glucose stimulation. The oxidation of 10 mM D-[U-14C]glucose was slightly enhanced by 0.1 and 1 mM tetracaine. The results indicate that tetracaine and lidocaine, at certain concentrations, can induce insulin release and that tetracaine potentiates secretion induced by other secretagogues. It is concluded that these effects may be associated with beta-cell functions related to the adrenergic receptors but probably not to cholinergic receptors.
Animals↗
Opposite effects of 5-hydroxytryptophan and 5-hydroxytryptamine on the function of microdissected ob/ob-mouse pancreatic islets.
The effects of 5-hydroxytryptamine and 5-hydroxytryptophan on insulin release and 45Ca2+ uptake in islets microdissected from ob/ob mice were studied. At a concentration of 4 mmol/l both compounds slightly stimulated insulin release at a low glucose concentration (3 mmol/l). Insulin release induced by 20 mmol/l D-glucose was inhibited by 4 mmol/l 5-hydroxytryptamine but potentiated by 4 mmol/l L-5-hydroxytryptophan. Mannoheptulose (20 mmol/l) blocked the combined effects of 20 mmol/l D-glucose and 4 mmol/l L-5-hydroxytryptophan on insulin release. 45Ca2+ uptake was inhibited by 4 mmol/l 5-hydroxytryptamine and stimulated by 4 mmol/l L-5-hydroxytryptophan. Mannoheptulose (20 mmol/l) did not affect the 45Ca2+ uptake induced by the latter. When 4 mmol/l L-5-hydroxytryptophan was present only during the 30-min preincubation period. 20 mmol/l-glucose-induced insulin release and 45Ca2+ uptake during a subsequent incubation period were inhibited. Externally added 5-hydroxytryptamine (4 mmol/l) did not change the effects of 4 mmol/l L-5-hydroxytryptophan on insulin release and 45Ca2+ uptake. It is concluded that, when added directly into the incubation medium, 5-hydroxytryptophan has effects on insulin release and 45Ca2+ uptake which are opposite to those observed when 5-hydroxytryptamine is added. These effects do not seem to be mediated by 5-hydroxytryptamine formed intracellularly from 5-hydroxytryptophan.
5-Hydroxytryptophan↗
Effects of selective alpha 1 and alpha 2 adrenoceptor active drugs on 86Rb+ efflux from pieces of rat parotid gland.
Minute pieces of rat parotid gland were used in studies of adrenergic regulation of K+ efflux using 86Rb+ as a probe for K+. Noradrenaline induced a concentration-dependent RB+ efflux, whereas the beta 1-selective agonist prenalterol was without effect. On the other hand, the beta 2-selective drug, terbutaline, at high concentrations displayed a small enhancement of Rb+-secretion. The selective alpha 1-adrenoceptor drug, phenylephrine, was as potent as noradrenaline, whereas the alpha 2-agonist clonidine had only a small effect. The noradrenaline-induced Rb+-efflux was effectively inhibited in the presence of prazosin, an alpha 1-blocker, whereas the alpha 2-antagonist, yohimbine, was roughly 50 times less potent. The results suggest that catecholamine-induced K+-secretion from the rat parotid gland is mediated via activation of post-synaptic alpha-adrenoceptors of the alpha 1-subtype.
Adrenergic alpha-Agonists↗
Effects of alpha-adrenoceptor agonists and antagonists on insulin secretion, calcium uptake, and rubidium efflux in mouse pancreatic islets.
Epinephrine, norepinephrine or the more selective alpha-2 adrenoceptor agonist, clonidine, inhibited insulin release from isolated pancreatic islets of lean mice or obese mice homozygous for the gene ob. Clonidine was highly effective at 0.1 mumol/l. In contrast, the preferential alpha-1 adrenoceptor agonist, phenylephrine, had no or only a modest effect at 10 mumol/l. The effects of norepinephrine or clonidine were counteracted by yohimbine, a preferential blocker of alpha-2 receptors, but not by prazosine, an alpha-1 receptor blocker. The glucose-stimulated uptake of 45Ca2+ in the islets was only consistently inhibited by epinephrine. This effect was counteracted by yohimbine. Clonidine had no effect on the release of 86Rb+ from preloaded islets. It is concluded that insulin secretion is suppressed by alpha-2 receptor agonism in the pancreatic beta-cells and that this effect is mediated by mechanisms other than the transmembrane fluxes of calcium or potassium ions.
Adrenergic alpha-Agonists↗
Mechanisms underlying the effects of 5-hydroxytryptamine and 5-hydroxytryptophan in pancreatic islets. A proposed role for L-aromatic amino acid decarboxylase.
Microdissected pancreatic islets of noninbred ob/ob mice were used in studies of 5-hydroxytryptamine (5-HT) and 5-hydroxytryptophan (5-HTP) effects on insulin release. The potentiating effect of 4 mM L-5-HTP on glucose-induced insulin release was inhibited by the decarboxylase inhibitors benserazide (100 microM), alpha-monofluoromethyldopa (10 or 100 microM), carbidopa (50 or 500 microM), and NSD 1015 (5 or 50 microM). Activation of L-aromatic amino acid decarboxylase by DL-m-tyrosine (4 mM) or DL-o-tyrosine (4 mM) potentiated glucose-induced insulin release, whereas L-dopa (4 mM) inhibited it. Glucose oxidation was unaffected by L-5-HTP but slightly stimulated by 5-HT. Glucose-induced efflux of 33Pi was reduced by 5-HT but not affected by 5-HTP. These results are compatible with the ideas that 5-HT inhibits glucose-induced insulin release by affecting early steps in the beta-cell stimulus-secretion coupling and that 5-HTP-potentiation of insulin release is probably mediated by the decarboxylase activity but is independent of the 5-HT formed.
5-Hydroxytryptophan↗
Biphasic modulation of K+ permeability in pancreatic islets during acute stimulation with glucose.
The regulation of 86Rb+ efflux (marker of K+ permeability) during acute secretagogic stimulation with glucose was studied with cultured as well as freshly isolated pancreatic islets from rats and freshly isolated islets from mice. A perifusion system with minimal dead-space and "flow-through" characteristics conductive to abrupt, steep increases in ambient glucose was combined with multiple samplings of effluent to achieve high temporal resolution. Under these conditions, acute increases in perifusate glucose concentration from 4 to 16.7 mM or from 1 to 27.8 mM effected a biphasic change of the 86Rb+ fractional efflux rate. A rapid reduction of 86Rb+ efflux was interrupted by an evanescent increase in 86Rb+ outflow, which appeared to be temporally coincident with the initiation of the first phase of stimulated insulin release. It is suggested that the glucose-induced biphasic oscillations in K+ permeability may contribute to the well-known initial biphasic changes in beta-cell membrane potential and insulin release during the inception of beta-cell stimulus secretion coupling.
Animals↗