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Biomedical subjects

E Gylfe

Publications and source records attributed to E Gylfe.

At least 163 records · Page 9Linked to original sources
PubMed1979

Calcium and pancreatic beta-cell function. 6. Glucose and intracellular 45Ca distribution.

Glucose stimulates the uptake of 45Ca into beta-cell-rich pancreatic islets isolated from ob/ob-mice. The distribution of the incorporated radioactivity was analysed by labelling the organelles with 45Ca in their cellular environment. The radioactive content of the organelles was measured after homogenization and fractionation of the islets under conditions preventing 45Ca redistribution. The 45Ca taken up in response to glucose appeared essentially in the secretory granule fraction and in that enriched in mitochondria. Modification of the 45Ca loading procedure, involving reduction of the oxygen tension and incubation volume, resulted in the disappearance of the glucose effect on the mitochondrial fraction whereas part of the stimulatory effect on the secretory granules persisted. Buffering of calcium by the secretory granules and mitochondria may be important for regulating the cytoplasmic Ca2+ involved in stimulus-secretion coupling.

Animals↗
PubMed1978

Protection of the pancreatic beta-cell glucoreceptor mechanism for insulin secretion during culture in chemically defined medium.

High concentrations of glucose have a protective effect on the glucoreceptor mechanism for insulin secretion during culture of pancreatic islets in chemically defined media. To study at what level glucose exerts this effect, insulin secretion from beta-cell-rich mouse pancreatic islets was measured before and after culture for 1 week in the presence of different substances. Before culture, glucose and inosine were potent stimulators, mannose and fructose were less potent and xylitol had no effect on secretion. Culture in 3mm-glucose resulted in a 10-fold decrease in the insulin response to glucose stimulation. A less marked decrease was noted after culture in 20mm- or 30mm-glucose. Inosine-stimulated secretion was much decreased after culture in high concentrations of glucose, whereas the responses to mannose or fructose were unchanged. After culture in 30mm-mannose, glucose-stimulated secretion was similar to that observed after culture in high concentrations of glucose, whereas the response to mannose had much decreased. There were no secretory responses to glucose or fructose after culture in 30mm-fructose, or to glucose or xylitol after culture in 30mm-xylitol. Culture in 10mm-inosine did not preserve any significant response to glucose or inosine. The insulin contents of islets and culture media were higher after culture in high concentrations of glucose, mannose or inosine than after culture in fructose, xylitol or low concentrations of glucose. It is suggested that glucose, and to some extent mannose, preserves the glucoreceptor mechanism for insulin secretion by influencing an early stage in glucose metabolism, presumably glucokinase activity.

Animals↗
PubMed1978

Calcium and pancreatic beta-cell function. 2. Mobilisation of glucose-sensitive 45Ca from perifused islets rich in beta-cells.

beta-Cell-rich pancreatic islets were microdissected from ob/ob-mice and loaded with 45Ca in the presence of 3 or 20 mM glucose. Subsequent measurements of the effluxes of radioactivity in a perifusion apparatus revealed that the slowly exchangeable 45Ca taken up in response to glucose was also preferentially mobilised by this compound. Glucose stimulation of 45Ca efflux was abolished after omission of calcium from the perifusion medium but persisted when insulin release was inhibited by prolonged starvation, addition of L-epinephrine or lowering of temperature. The presence of a stimulated efflux of radioactivity even under conditions of inhibited insulin release indicates that sources other than beta-granules ejected by exocytosis contribute to the additional 45Ca released after raising the glucose concentration of the perifusion medium. It is suggested that the beta-cell depolarisation as such may account for part of the 45Ca mobilised by glucose.

Animals↗
PubMed1978

Metabolism of cold-stored pancreatic islets.

A previous study showed that the ability of glucose to stimulate insulin release was retained in islets stored at 8 degrees C for one week provided that glucose was present in a high concentration in the storage medium. The metabolic properties of islets stored in the cold have now been further explored in an attempt to clarify the protective effect of glucose. During storage in the cold the islet formation of 3H2O from (5--3H) glucose and oxygen consumption were only a few per cent of that of fresh islets whereas the putake of 86Rb+ was 20--48%. Rewarming the cold-stored islets to 37 degrees C after one week of cold-storage restored the 86Rb+ uptake, the formation of 3H2O and 14CO2 from labelled glucose and oxygen consumption to 75, 80, 60 and 40% respectively of fresh islet levels. The results emphasize the usefulness of cold-storage for preservation of functionally intact isolated islets.

Animals↗
PubMed1978

Calcium and pancreatic beta-cell function: glucose stimulation uptake of lanthanum-displaceable 45-Ca from low or normal calcium-containing media.

The uptake of 45Ca was studied in beta-cell-rich pancreatic islets microdissected from ob/ob-mice. Glucose stimulated 45Ca incorporation in a lanthanum-displaceable pool remaining after correction for the extracellular space occupied by sucrose. It is suggested that the glucose effect on the lanthanum-displaceable calcium is the cause rather than the result of the secretion of insulin since it could be demonstrated also in the presence of only trace amounts of extracellular calcium.

Animals↗
PubMed1978

Glucose inhibition of 45Ca efflux from pancreatic islets.

Pancreatic islets were microdissected from ob/ob mice, loaded for 2 h with 45Ca and perfused with calcium-deficient medium. Irrespective of the glucose and calcium concentrations in the loading medium, increased glucose in the perfusion medium resulted in reduced amounts of radioactivity in the perfusate. A glucose inhibition of 45Ca washout was also evident when the specific radioactivity of the islets approached that of the labeling medium, indicating that the effect was not simply due to isotopic dilution. The depression of 45Ca washout diminished after culture of the islets in a serum-free medium and it was absent in islets taken from mice homozygous for the gene diabetes. The glucose effect became less pronounced when 50 micron D-600, an inhibitor of the calcium inward transport, was added to the calcium-deficient perfusion medium and abolished in the presence of 20 mM Ca-EGTA. The inhibition of the 45Ca washout observed is not necessarily due to a direct glucose interaction with the outward calcium transport but may also result from stimulation of the uptake and intracellular trapping of the cation.

Animals↗
PubMed1978

Collagenase isolation and 45Ca efflux studies of human islets of Langerhans.

22 human pancreases were removed soon after circulatory arrest from donors aged 15--63 years. Part of the pancreas was used for isolation of islets by the collagenase technique. The mean yield +/- SEM, expressed as the number of islets isolated from 4 g pancreas was 79 +/- 15. The yield varied considerably even when the pancreas was removed immediately after circulatory arrest and the histology was normal, and there was no correlation with the age of the donors. The islet content of insulin (ng/microgram dry islet) was 8.5 +/- 1.2 (mean +/- SEM). Isolated islets were loaded with 45Ca in the presence of 20 mM glucose and placed in a perfusion apparatus for further studies of the 45Ca washout. The decrease of washout of radioactivity in Ca2+-deficient medium offers support for the existence of a Ca2+-Ca2+ exchange process. When added in a concentration of 20 mM, glucose tended to stimulate 45Ca efflux in perfusion medium of ordinary ionic composition but inhibited this process when the medium was deficient in Ca2+. Exposure to the calcium ionophore X-537A resulted in immediate stimulation of of 45Ca efflux from human islets as previously observed for islets from rats and mice. This suggests that Ca2+ has a direct regulatory role for insulin release also in humans.

Adolescent↗
PubMed1978

Association between 5-hydroxytryptamine release and insulin secretion.

The efflux of radioactivity after loading with trace amounts of tritiated 5-hydroxytryptamine ([3H]5-HT) or 5-hydroxytryptophan ([3H]5-HTP) was studied in perifused beta-cell-rich pancreatic islets from ob/ob mice. Analysis of the effluent revealed that more than 90% of the radioactivity was released as [3H]5-HT after loading with [3H]5-HTP. Increasing the concentration of glucose in the perifusion medium from 3 to 20 mmol/l enhanced the efflux when islets from fed mice were used and this effect was potentiated by the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX). Whereas 20 mM-glucose alone did not stimulate the efflux of 5-HT from islets isolated from mice starved for 3 days, a stimulatory effect was observed in the presence of IBMX. Stimulation of the efflux of radioactivity by glucose was inhibited if calcium was omitted from or adrenaline added to the medium. The results are consistent with the concept of exocytotic release of 5-HT occurring in response to stimulation of insulin secretion, although basal non-exocytotic transport must also be occurring across the beta-cell membrane.

5-Hydroxytryptophan↗
PubMed1977

Specific glucose protection of pancreatic beta-cell function during culture in chemically defined medium.

Microdissected pancreatic islets from non-inbred ob/ob-mice were cultured for 7 days in modified tissue culture medium 199 lacking serum. When 3 mM glucose was present during culture little or no insulin response to glucose stimulation was observed during the following incubation. Culture with 18 mM glucose on the other hand resulted in good preservation of glucose-stimulated insulin release, especially if release into the culture medium had been inhibited by lack of Ca++. High concentrations of leucine or its non-metabolizable analogue, 2-aminobicyclo(2,2,1)heptane-2-carboxylic acid (BCH), stimulated insulin release into the culture medium but did not preserve glucose-stimulated insulin release. When compared to previously published fresh-islet levels, culture with 3 mM glucose alone or in combination with high concentrations of leucine or BCH resulted in a substantial loss of beta-cell insulin. This loss was less marked after culture with 18 mM glucose, and completely abolished if no Ca++ was included in the high glucose medium. The data indicate that glucose has a specific effect in protecting some glucoreceptor mechanism of the beta-cells during culture.

Amino Acids↗
PubMed1976

Interactions between the metabolism of L-leucine and D-glucose in the pancreatic beta-cells.

Beta-Cell-rich pancreatic islets microdissected from obese-hyperglycemic mice were used to study interactions between the metabolism of L-leucine and D-glucose. L-leucine reduced the islet content of aspartic acid whereas D-glucose, when added to L-leucine-incubated islets, increased the contents of aspartic acid and gamma-aminobutyric acid (GABA). D-glucose also increased the incorporation of L-leucine carbon into aspartic acid, GABA and glutamic acid suggesting stimulation of a malate shuttle mechanism. When expressed per mole of the individual amino acids, the incorporation of L-leucine carbon into GABA was 2.5-4 times higher than into glutamic acid indicating intracellular compartmentation of the latter amino acid. Both L-leucine and D-leucine stimulated 14CO2 production from 14C-labelled D-glucose. L-leucine did not affect 3H2O production from tritiated D-glucose. The present data do not indicate a role of other amino acids or D-glucose in L-leucine-stimulated insulin release.

Animals↗
PubMed1976

Maintenance of insulin release from pancreatic islets stored in the cold for up to 5 weeks.

Insulin content and release were measured from hand-dissected pancreatic islets from noninbred ob/ob mice after 1-5 wk storage in tissue culture medium 199 at various temperatures and glucose concentrations. After storage of islets for 1 wk at 37 degrees, 22 degrees, or 8 degrees C in 18 mM glucose medium and preincubation with 1 mM glucose, glucose-stimulated insulin release during the subsequent incubation was only 20-35% of that of fresh islets. The addition of a 4-h period at 37 degrees C with 18 mM glucose between the cold storage and perincubation restored glucose-stimulated insulin release from 8 degrees C stored islets to fresh-islet levels. Release throughout the 1-18 mM glucose range was strikingly parallel to that of fresh islets. Exposure of fresh islets to the same 4-h period increased basal release but did not affect maximal release. When islets were stored at 8 degrees C with 18 mM glucose for more than 1 wk, a short period at 37 degrees C every week was necessary for maintenance of release. After 5 wk of this procedure, glucose-stimulated insulin release was one-third that of fresh islets, or similar to that of islets stored for only 1 wk at 37 degrees C. Storage at 8 degrees C for 1 wk with 3 mM glucose, or continuously for 3 or 5 wk with 18 mM glucose, maintained islet insulin content, whereas release was lost. Thus, glucose-stimulated insulin release is best maintained by storage of pancreatic islets in tissue culture medium with a high concentration of glucose at 8 degrees C with short weekly periods at 37 degrees C.

Animals↗
PubMed1975

Function of microdissected pancreatic islets cultured in a chemically defined medium. I. Insulin content and release.

Microdissected pancreatic islets from non-inbred ob/ob-mice were cultured for 6 or 7 days in serum-free tissue culture medium 199. The insulin content of the islets decreased 60% during culture in 17 mM or 28 mM glucose and about 70% in the presence of 3.3 mM or 5.6 mM glucose. At the end of a culture period in high glucose, the sum of the insulin in the islet plus that in the culture medium was almost twice as high as the insulin content of fresh islets, indicating an active insulin biosynthesis. The maximal insulin response to glucose after culture in 17 mM or 28 mM glucose was about 40% of that in fresh islets; after culture in 3.3 mM glucose it was 10%. Half-maximal stimulation was observed at a glucose concentration of 5 mM for islets cultured with high glucose as compared to 9 mM for fresh islets. Like glucose, glibenclamide was a more effective insulin stimulator after culture with a high glucose concentration than with a low one. However, leucine-induced insulin release was not affected by the glucose concentration in the preceding culture medium. Whereas potentiation of glucose-stimulated release by arginine or dibutyryl-cAMP was independent of glucose concentration during the culture, theophylline released three times more insulin when the islets had been cultured with high glucose.

Animals↗
PubMed1975

The heat production of pancreatic beta-cells stimulated by glucose.

A recently developed batch microcalorimeter was used for studying heat production in beta-cell-rich pancreatic islets isolated from obese-hyperglycemic mice. In the absence of glucose, the rate of heat production was 50 nW/islet increasing to 90 nW/islet when the islets were exposed to 20 mM glucose. The data obtained are consistent with an increase in the caloric value of oxygen with glucose concentration, as might be expected when the beta-cells utilize proportionally more carbohydrate as a source of energy.

Animals↗