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Biomedical subjects

J Sehlin

Publications and source records attributed to J Sehlin.

At least 55 records · Page 3Linked to original sources
PubMed1988

Effects of Cl- deficiency on the membrane potential in mouse pancreatic beta-cells.

The membrane potential of mouse pancreatic beta-cells was measured with microelectrodes. In the resting cell (3 mM D-glucose), the membrane potential was -63 +/- 3 mV (mean +/- S.E. for four experiments). In the presence of 3 mM D-glucose, total Cl- substitution by isethionate induced a depolarization by 3-4 mV, and readmission of Cl- induced a hyperpolarization by 3-5 mV. At 10 mM glucose, reduction of Cl- to 12 mM by substituting isethionate for Cl- reversibly shifted the repolarization potential by 6-9 mV in the positive direction and stimulated the burst activity during the initial 2-3 min by increasing the fraction of plateau phase. This was followed by a gradual inhibition of electrical activity, including decrease in fraction of plateau phase and slow wave amplitude. Total substitution of Cl- by isethionate or methyl sulphate reversibly shifted the repolarization potential by 3-4 mV in the positive direction and rapidly inhibited the electrical burst pattern without any initial stimulation. Glucose-induced (10 mM) insulin release (15 min) and 45Ca2+ uptake (3 min) were strongly inhibited by reducing the Cl- concentration to 10 mM (isethionate as substitute) and were further inhibited by further reduction of the Cl- concentration. It is suggested that beta-cells are equipped with on electrogenic Cl- flux, which can affect the burst pattern of electrical activity. The inhibitory effects of Cl- substitution may be explained by an influence of Cl- on the voltage-controlled Ca2+ channels.

Animals↗
PubMed1988

Furosemide causes acute and long-term hyperglycaemia and reduces glucose tolerance in mice.

The effect of furosemide on carbohydrate metabolism was studied in mice. Single-dose administration (200 mg kg-1 body weight) resulted in transient hyperglycaemia and a rise in the glucose/insulin ratio within 60 min. The glucose tolerance was impaired with elevated serum glucose and reduced insulin response 2 h after the furosemide injection, but had recovered within 24 h. In mice made hypoglycaemic by prior injection of insulin, the basal serum glucose and the glucose tolerance were impaired 22 h after the injection of furosemide. It is suggested that furosemide has both acute and long-term effects on carbohydrate metabolism in mice and that, at least in part, this is due to reduced insulin secretion. Glucose may protect against the diabetogenic action of furosemide.

Animals↗
PubMed1988

Evidence that an L-fucose-containing component in the beta-cell plasma membrane is involved in the regulation of glucose-induced insulin release.

The effect of the L-fucose-selective lectin Ulex Europeus I (UEA I), a blocker of the Na+, K+, Cl- co-transport system in the kidney, was tested on insulin secretion from isolated beta-cell-rich pancreatic islets. UEA I at doses from 50 to 100 micrograms ml-1 significantly reduced the glucose-induced (20 mmol l-1) insulin release whereas the basal (3 mmol l-1) release was unaffected. The inhibitory effect of 100 micrograms ml l-1 UEA I was completely abolished by 10 mmol l-1 L-fucose. The data suggest that an L-fucose-containing structure in the beta-cell plasma membrane participates in the regulation of glucose-induced insulin release. This structure may be similar to the L-fucose-containing glycoprotein in the kidney tubules that is believed to be the Na+, K+, Cl- cotransporter.

Animals↗
PubMed1988

Evidence for co-transport of sodium, potassium and chloride in mouse pancreatic islets.

1. The presence of a loop diuretic-sensitive co-transport system for Na+, K+ and Cl- was tested in isolated pancreatic islets. 2. Substitution of Cl- with the impermeant anion isethionate or addition of frusemide both reduced the ouabain-resistant islets uptake of 86Rb+ (K+ marker) without affecting the ouabain-sensitive uptake or equilibrium content of 86Rb+. The effects of Cl- substitution and frusemide were overlapping. 3. D-Glucose reduced the ouabain-resistant islets uptake of 86Rb+. This effect was additive to the effect of Cl- substitution or frusemide. 4. Substitution of Cl- with isethionate or addition of frusemide both reduced the efflux of 86Rb+ from the islets. These effects were additive to the reduction of 86Rb+ efflux induced by D-glucose. 5. Substitution of K+ or Na+ with choline reduced the equilibrium content of 36Cl- in the pancreatic islets. 6. These data are compatible with the operation in the pancreatic beta-cells of a loop diuretic-sensitive co-transport system for Na+, K+ and Cl-, that may serve as an inwardly directed Cl- pump.

Animals↗
PubMed1988

Furosemide reduces insulin release by inhibition of Cl- and Ca2+ fluxes in beta-cells.

The effect of furosemide on insulin release, glucose oxidation, 36Cl- fluxes, and 45Ca2+ uptake was studied in isolated, beta-cell-rich pancreatic islets from ob/ob mice. Low concentrations of furosemide (0.01-0.1 mM) reduced the glucose-induced insulin release, whereas high doses (1-10 mM) increased basal and glucose-induced release. Furosemide at concentrations that reduced glucose-induced insulin release (0.01-0.1 mM) did not affect the islet production of 14CO2 from D-[U-14C]glucose. The influx rate and equilibrium content of 36Cl- were reduced by furosemide, whereas the basal and glucose-stimulated 36Cl- efflux rates were unaffected. The glucose-induced (10 mM) uptake of 45Ca2+ was inhibited by furosemide. It is suggested that the diabetogenic action of furosemide may be due, at least in part, to direct inhibition of insulin release from the pancreatic beta-cells. This may be caused primarily by inhibition of an inwardly directed Cl- pump, leading to a reduced transmembrane electrochemical gradient for chloride in the beta-cells. This reduced gradient in combination with unaltered Cl- permeability may lead to decreased total outward Cl- transport, a factor associated with stimulated calcium uptake and insulin release.

Animals↗
PubMed1987

Stereoselective inhibition of chloride transport by loop diuretics in pancreatic beta-cells.

The effects of loop diuretics on 36Cl- uptake was tested in isolated beta-cell-rich pancreatic islets. Bumetanide reduced the 36Cl- influx and the levorotatory form of ozolinone reduced both the influx and equilibrium content of 36Cl- in the islets, whereas the dextrorotatory form was largely inactive. The data suggest that the beta-cells are equipped with a loop diuretic-sensitive system for 36Cl- uptake and that this system is confined to a sterically well-defined structure.

Animals↗
PubMed1987

Effect of perchlorate on calcium uptake and insulin secretion in mouse pancreatic islets.

Microdissected beta-cell-rich pancreatic islets of non-inbred ob/ob mice were used in studies of how perchlorate (CIO4-) affects stimulus-secretion coupling in beta-cells. CIO4- at 16 mM potentiated D-glucose-induced insulin release, without inducing secretion at non-stimulatory glucose concentrations. The potentiation mainly applied to the first phase of stimulated insulin release. In the presence of 20 mM-glucose, the half-maximum effect of CIO4- was reached at 5.5 mM and maximum effect at 12 mM of the anion. The potentiation was reversible and inhibitable by D-mannoheptulose (20 mM) or Ca2+ deficiency. CIO4- at 1-8 mM did not affect glucose oxidation. The effects on secretion were paralleled by a potentiation of glucose-induced 45Ca2+ influx during 3 min. K+-induced insulin secretion and 45Ca2+ uptake were potentiated by 8-16 mM-CIO4-. The spontaneous inactivation of K+-induced (20.9 mM-K+) insulin release was delayed by 8 mM-CIO4-. The anion potentiated the 45Ca2+ uptake induced by glibenclamide, which is known to depolarize the beta-cell. Insulin release was not affected by 1-10 mM-trichloroacetate. It is suggested that CIO4- stimulates the beta-cell by affecting the gating of voltage-controlled Ca2+ channels.

Animals↗
PubMed1987

Evidence for voltage-dependent C1- permeability in mouse pancreatic beta-cells.

Microdissected beta-cell-rich pancreatic islets from ob/ob-mice were used in studies of transmembrane 36Cl- efflux. The mean rate coefficient for 36Cl- efflux was stable at 0.158 min-1 during the initial 10 min. Depolarization of the beta-cell plasma membrane by acute increases in extracellular K+ (5-130 mM) stimulated the 36Cl- efflux in a concentration-dependent manner. Glucose-induced (20 mM) and K+-induced increases in 36Cl- efflux were largely overlapping, but even at 135.9 mM K+, glucose slightly further enhanced the 36Cl- efflux rate. The data suggest that pancreatic beta-cells are equipped with a voltage-dependent Cl- permeability, that glucose-induced increase in Cl- permeability may, at least partly, be mediated by primary membrane depolarization, and that glucose in addition may activate other mechanisms for beta-cell Cl- transport.

Animals↗
PubMed1987

Effects of substrates for aromatic L-amino acid decarboxylase on insulin secretion.

It has been shown that substrates for aromatic L-amino acid decarboxylase potentiate glucose-induced insulin release. Microdissected islets of obese-hyperglycemic mice (Umeå ob/ob) have now been used in a study of the effects of decarboxylase substrates on insulin release induced by secretagogues other than glucose. L-5-hydroxytryptophan (L-5-HTP) at 4 mmol/l potentiated the effect of 1 mumol/l glibenclamide, 20 mmol/l D,L-glyceraldehyde or 20 mmol/l K+, but not that of 50 mumol/l chloromercuribenzene-p-sulphonic acid. The potentiating effect of 4 mmol/l L-5-HTP, 4 mmol/l D,L-m-tyrosine, or 4 mmol/l D,L-o-tyrosine on insulin release induced by 20 mmol/l L-leucine was inhibited by 0.1 mmol/l benserazide. Benserazide did not reduce the effect of 10 mmol/l L-glutamine on L-leucine-induced insulin release. L-dihydroxyphenylalanine inhibited glucose-induced insulin secretion at 0.1 mmol/l with a tendency towards a reduction also at lower concentrations. The findings support the hypothesis that increased activity of aromatic L-amino acid decarboxylase can stimulate islet B cell function.

5-Hydroxytryptophan↗
PubMed1987

Abnormalities in glucose-stimulated insulin release, 45Ca uptake, and 86Rb efflux in diabetic Chinese hamster islets.

We loaded islets from normal and diabetic Chinese hamsters with 86Rb (an analogue for K+) and measured 86Rb efflux during stimulation with 20 mM D-glucose. Genetically diabetic Chinese hamsters were selected from a subline (L) known for subnormal pancreatic insulin release and excessive pancreatic glucagon release in vitro. 86Rb accumulation in 1 mM glucose was normal in the diabetic islets. Similar to the pattern of 86Rb efflux previously seen from normal rat and mouse islets, 20 mM glucose suppressed 86Rb efflux within 1-2 min, and efflux remained suppressed until return to 1 mM glucose in both normal and diabetic hamster islets. After the first 2 min of 20 mM glucose, suppression of 86Rb efflux was somewhat greater in the diabetic hamster islets than in the normals. In addition, glucose-stimulated insulin release and 45Ca uptake were significantly reduced in the diabetic islets. Therefore, in the diabetic hamster islets, there is at least no impairment in the initial suppression of 86Rb efflux by glucose. This suggests that the diabetic beta-cells recognize glucose and carry out the initial steps in the stimulus-secretion coupling sequence normally. The later, excessive suppression of 86Rb efflux may be due to impaired Ca2+-induced changes in 86Rb efflux, suggesting that defective regulation of intracellular Ca2+ activity, rather than defective regulation of K+ permeability, may lead to the impaired insulin secretion.

Animals↗
PubMed1987

Hyaluronan in the middle ear of the rat. The normal distribution of hyaluronan and the clearance of exogenously administered hyaluronan from the middle ear.

The content of hyaluronan (HA), a common connective tissue component, was determined in well defined areas of the rat middle ear. The HA concentration in the pars flaccida of the tympanic membrane was considerably greater than in the pars tensa and areas on the medial wall of the middle ear cavity. The fate of exogenous HA introduced into the middle ear was also studied in rats. Tritium-labelled HA disappeared through the Eustachian tube (ET) and was followed by analysis of the nasopharyngeal secretion. The radioactivity in the secretion reached a peak at 3 h and decreased to almost zero within 12 h, indicating that most of the HA was removed. By autoradiography and direct analysis of the HA concentration and molecular weight distribution the fate of HA after obstruction of the ET was followed. Radioactive HA was confined to the middle ear and no uptake into surrounding tissues could be traced by autoradiography 4 days after application. The amount of HA that could be recovered from the middle ear was constant for up to 6 days. Analysis of the molecular weight distribution of the deposited HA indicated only slow degradation during these 6 days.

Animals↗
PubMed1986

Effect of intracellular alkalinization on pancreatic islet calcium uptake and insulin secretion.

Microdissected beta-cell-rich pancreatic islets of ob/ob mice were used in studies of the relationship between intracellular pH (pHi) and 45Ca2+ uptake and insulin release. Stepwise increases in extracellular pH (pHo) from 6.80 to 8.00 resulted in a parallel, although less pronounced, elevation of pHi from 7.24 to 7.69. Experimental conditions that alkalinize the islet cell interior, i.e. addition of 5 mM-NH4+, sudden withdrawal of extracellular bicarbonate buffer or increase in pHo, induced insulin secretion in the absence of other types of secretory stimulation (1 mM-D-glucose). Intracellular acidification by lowering pHo below 7.40 or sudden addition of bicarbonate buffer did not induce insulin secretion. The removal of extracellular bicarbonate buffer, increase in pHo from 7.40 to 8.00, or the addition of 5 mM-L-5-hydroxytryptophan or 5 mM-NH4+, which all alkalinize the islet cells and induce insulin secretion, also increased the La3+-non-displaceable 45Ca2+ uptake in the presence of 1 mM-D-glucose. The results suggest that intracellular alkalinization in beta-cells can trigger insulin secretion. Taken together with the fact that D-glucose increases pHi in the islet cells, the results also point to the possibility that alkalinization may be a link in the stimulus-secretion coupling sequence in beta-cells.

5-Hydroxytryptophan↗
PubMed1986

Measurements of serum glucose using the luciferin/luciferase system and a liquid scintillation spectrometer.

A single-step assay for serum glucose measurements is described. The assay is based on the phosphorylation of D-glucose by glucokinase and the measurement of ATP consumption by firefly luciferase. The luminescence is recorded in an ordinary liquid scintillation spectrometer. The use of stable reagents and a stable final signal (light emission) makes it possible to analyze a large number of samples in each assay run. The assay is of particular value when repeated serum glucose determinations are performed on samples from small laboratory animals.

Adenosine Triphosphate↗
PubMed1986

Glucose reduces both Rb+ influx and efflux in pancreatic islet cells.

Microdissected, beta-cell-rich pancreatic islets from ob/ob mice were used in studies of 86Rb+ transport. D-Glucose (20 mM) induced a biphasic reduction in 86Rb+ efflux. The reduction stabilized within 10 min at 34% of the efflux rate at zero glucose. The initial 86Rb+ uptake (5 min) was dose-dependently reduced by ouabain with maximum inhibition at 1 mM. D-Glucose (20 mM) did not affect the ouabain-sensitive 86Rb+ influx but markedly reduced (48%) the ouabain-resistant isotope influx. The results suggest that D-glucose does not affect the Na+/K+ pump in pancreatic beta-cells and that the glucose-sensitive K+-transporting modalities (K+ channels) in the beta-cells can mediate both inward and outward K+ flux.

Animals↗
PubMed1986

Aromatic amino acids and pancreatic islet function: a comparison of L-tryptophan and L-5-hydroxytryptophan.

L-Tryptophan (4 mM) did not affect insulin release at 3 mM glucose but strongly potentiated glucose-induced (10 mM) insulin release in microdissected ob/ob mouse islets. The effect was concentration dependent with half-maximum at about 5 mM. 10 mM L-glutamate also enhanced the effect of 10 mM D-glucose on insulin release but L-phenylalanine, L-tyrosine, L-alanine, glycine and L-glutamine did not. 0.1 mM benserazide and 0.1 mM alpha-monofluoromethyldopa did not inhibit the effect of L-tryptophan. 1 mM aminooxyacetate reduced the potentiating effect of L-tryptophan but not that of L-5-hydroxytryptophan. 10 mM indole pyruvate stimulated basal insulin release but inhibited the effect of glucose. 10 mM L-glutamine did not enhance the stimulatory effect of indole pyruvate. 10 mM L-5-hydroxytryptophan reduced the effect of 10 mM L-glutamine on glucose oxidation. L-5-Hydroxytryptophan did not influence 14CO2 production from islets preloaded with [14C]glutamine but reduced the oxidation rate when [14C]glutamine was present in the incubation medium. Both L-tryptophan and L-5-hydroxytryptophan potentiate insulin release. The underlying mechanisms probably differ but do not seem to involve transaminations. The effect of L-5-hydroxytryptophan may be coupled to the activity of aromatic L-amino acid decarboxylase.

5-Hydroxytryptophan↗
PubMed1986

Rubidium uptake by mouse pancreatic islets exposed to 6-hydroxydopamine, ninhydrin, or other generators of hydroxyl radicals.

The purpose was to study the toxicity of drugs known to generate free radicals on isolated pancreatic islets. The accumulation of 86Rb+ by mouse pancreatic islets was measured in vitro. Exposing the islets to 6-hydroxydopamine, ninhydrin, or phenazine methosulphate+NADH inhibited the Rb+ uptake, whereas paraquat or acetylphenylhydrazine had no effect. This effect of 6-hydroxydopamine was prevented by either of the hydroxyl radical scavengers, sodium benzoate and mannitol, but not by the non-scavenger, urea; ninhydrin was partially protected against by mannitol but not by benzoate. Protection against 6-hydroxydopamine was also afforded by D-glucose but not by L-glucose or 3-O-methyl-D-glucose; none of the sugars protected against ninhydrin. In damaging islet beta-cells and in being protected against by D-glucose, 6-hydroxydopamine closely resembles the diabetogenic drug, alloxan. It is suggested that protection against alloxan may involve both glucose metabolism and the interaction of glucose with its membrane-located carrier, while protection against 6-hydroxydopamine appears to be unrelated to the hexose carrier mechanism.

Animals↗
PubMed1986

Potassium and chloride fluxes are involved in volume regulation in mouse pancreatic islet cells.

Potassium and chloride transport were measured in beta-cell-rich islets from ob/ob-mice using 36Cl- and 86Rb+ (K+-analogue). Reduction of the osmolarity from the normal 317 mosm l-1 to 180 mosm l-1 reduced the apparent content of K+ and Cl-. Hypo-osmolarity had no effect on the ouabain-sensitive portion of the Rb+ influx (Na+/K+ pump), but reduced the ouabain-resistant portion of the influx. Hypo-osmolarity also strongly increased the Rb+ efflux rate. Both tetracaine (0.5 mM) and glibenclamide (20 microM), which increase the osmotic resistance of pancreatic beta cells, significantly potentiated the reduction in apparent K+ content induced by hypo-osmolarity. This study suggests that the volume regulation in pancreatic beta cells is partly due to K+ and Cl- flux and that glibenclamide and tetracaine increase the osmotic resistance of the beta cells by affecting such ion transport.

Animals↗