Biomedical subjects

M L McDaniel

Publications and source records attributed to M L McDaniel.

At least 19 recordsLinked to original sources

PubMed1992

Nitric oxide and cyclic GMP formation induced by interleukin 1 beta in islets of Langerhans. Evidence for an effector role of nitric oxide in islet dysfunction.

Treatment of pancreatic islets with interleukin 1 (IL-1) results in a time-dependent inhibition of glucose-stimulated insulin secretion which has recently been demonstrated to be dependent on the metabolism of L-arginine to nitric oxide. In this report IL-1 beta is shown to induce the accumulation of cyclic GMP (cGMP) in a time-dependent fashion that mimics the time-dependent inhibition of insulin secretion by IL-1 beta. The accumulation of cGMP is dependent on nitric oxide synthase activity, since NG-monomethyl-L-arginine (a competitive inhibitor of nitric oxide synthase) prevents IL-1 beta-induced cGMP accumulation. cGMP formation and nitrite production induced by IL-1 beta pretreatment of islets are also blocked by the protein synthesis inhibitor, cycloheximide. The formation of cGMP does not appear to mediate the inhibitory effects of IL-1 beta on insulin secretion since a concentration of cycloheximide (1 microM) that blocks IL-1 beta-induced inhibition of glucose-stimulated insulin secretion and nitric oxide formation does not prevent cGMP accumulation, thus dissociating the two events. By using e.p.r. spectroscopy, IL-1 beta is shown to induce the formation of a g = 2.04 iron-nitrosyl feature in islets which is prevented by cycloheximide, demonstrating the requirement of protein synthesis for IL-1 beta-induced nitric oxide formation. Iron-nitrosyl complex-formation by islets confirms that IL-1 beta induces the generation of nitric oxide by islets, and provides evidence indicating that nitric oxide mediates destruction of iron-sulphur clusters of iron-containing enzymes. Consistent with the destruction of iron-sulphur centres is the finding that pretreatment of islets with IL-1 beta results in an approx. 60% inhibition of mitochondrial oxidation of D-glucose to CO2. Inhibition of islet glucose oxidation appears to be mediated by nitric oxide since both NMMA and cycloheximide prevent IL-1 beta-induced inhibition of glucose oxidation. These results show that IL-1 beta-induced nitric oxide formation parallels the ability of IL-1 beta to inhibit glucose-stimulated insulin secretion by islets, and that protein synthesis is required for IL-1 beta-induced nitric oxide formation. These results also suggest that nitric oxide mediates IL-1 beta-induced inhibitory effects on the pancreatic beta-cell by functioning as an effector molecule responsible for the destruction of iron-sulphur centres of iron-containing proteins, resulting in an impairment of mitochondrial function.

Amino Acid Oxidoreductases↗

PubMed1992

Parallel effects of arachidonic acid on insulin secretion, calmodulin-dependent protein kinase activity and protein kinase C activity in pancreatic islets.

A potential role of arachidonic acid in the modulation of insulin secretion was investigated by measuring its effects on calmodulin-dependent protein kinase and protein kinase C in islet subcellular fractions. The results were interpreted in the light of arachidonic acid effects on insulin secretion from intact islets. Arachidonic acid could replace phosphatidylserine in activation of cytosolic protein kinase C (K0.5 of 10 microM) and maximum activation was observed at 50 microM arachidonate. Arachidonic acid did not affect the Ca2+ requirement of the phosphatidylserine-stimulated activity. Arachidonic acid (200 microM) inhibited (greater than 90%) calmodulin-dependent protein kinase activity (K0.5 = 50-100 microM) but modestly increased basal phosphorylation activity (no added calcium or calmodulin). Arachidonic acid inhibited glucose-sensitive insulin secretion from islets (K0.5 = 24 microM) measured in static secretion assays. Maximum inhibition (approximately 70%) was achieved at 50-100 microM arachidonic acid. Basal insulin secretion (3 mM glucose) was modestly stimulated by 100 microM arachidonic acid but in a non-saturable manner. In perifusion secretion studies, arachidonic acid (20 microM) had no effect on the first phase of glucose-induced secretion but nearly completely suppressed second phase secretion. At basal glucose (4 mM), arachidonic acid induced a modest but reproducible biphasic insulin secretion response which mimicked glucose-sensitive secretion. However, phosphorylation of an 80 kD protein substrate of protein kinase C was not increased when intact islets were incubated with arachidonic acid, suggesting that the small increases in insulin secretion seen with arachidonic acid were not mediated by protein kinase C. These data suggest that arachidonic acid generated by exposure of islets to glucose may influence insulin secretion by inhibiting the activity of calmodulin-dependent protein kinase but probably has little effect on protein kinase C activity.

Animals↗

PubMed1992

Interleukin 1 beta induces the formation of nitric oxide by beta-cells purified from rodent islets of Langerhans. Evidence for the beta-cell as a source and site of action of nitric oxide.

Nitric oxide has recently been implicated as the effector molecule that mediates IL-1 beta-induced inhibition of glucose-stimulated insulin secretion and beta-cell specific destruction. The pancreatic islet represents a heterogeneous cell population containing both endocrine cells (beta-[insulin], alpha-]glucagon], gamma[somatostatin], and PP-[polypeptide] secreting cells) and non-endocrine cells (fibroblast, macrophage, endothelial, and dendritic cells). The purpose of this investigation was to determine if the beta-cell, which is selectively destroyed during insulin-dependent diabetes mellitus, is both a source of IL-1 beta-induced nitric oxide production and also a site of action of this free radical. Pretreatment of beta-cells, purified by FACS with IL-1 beta results in a 40% inhibition of glucose-stimulated insulin secretion that is prevented by the nitric oxide synthase inhibitor, NG-monomethyl-L-arginine (NMMA). IL-1 beta induces the formation of nitric oxide by purified beta-cells as evidenced by the accumulation of cGMP, which is blocked by NMMA. IL-1 beta also induces the accumulation of cGMP by the insulinoma cell line Rin-m5F, and both NMMA as well as the protein synthesis inhibitor cycloheximide prevent this cGMP accumulation. Iron-sulfur proteins appear to be intracellular targets of nitric oxide. IL-1 beta induces the formation of an iron-dinitrosyl complex by Rin-m5F cells indicating that nitric oxide mediates the destruction of iron-sulfur clusters of iron containing enzymes. This is further demonstrated by IL-1 beta-induced inhibition of glucose oxidation by purified beta-cells, mitochondrial aconitase activity of dispersed islet cells, and mitochondrial aconitase activity of Rin-m5F cells, all of which are prevented by NMMA. IL-1 beta does not appear to affect FACS-purified alpha-cell metabolic activity or intracellular cGMP levels, suggesting that IL-1 beta does not exert any effect on alpha-cells. These results demonstrate that the islet beta-cell is a source of IL-1 beta-induced nitric oxide production, and that beta-cell mitochondrial iron-sulfur containing enzymes are one site of action of nitric oxide.

Aconitate Hydratase↗

PubMed1992

Aminoguanidine, a novel inhibitor of nitric oxide formation, prevents diabetic vascular dysfunction.

Increased blood flow and vascular leakage of proteins preferentially affect tissues that are sites of diabetic complications in humans and animals. These vascular changes in diabetic rats are largely prevented by aminoguanidine. Glucose-induced vascular changes in nondiabetic rats are also prevented by aminoguanidine and by NG-monomethyl-L-arginine (NMMA), an established inhibitor of nitric oxide (NO.) formation from L-arginine. Aminoguanidine and NMMA are equipotent inhibitors of interleukin-1 beta-induced 1) nitrite formation (an oxidation product of NO.) and cGMP accumulation by the rat beta-cell insulinoma cell line RINm5F, and 2) inhibition of glucose-stimulated insulin secretion and formation of iron-nitrosyl complexes by islets of Langerhans. In contrast, NMMA is approximately 40 times more potent than aminoquanidine in elevating blood pressure in nondiabetic rats. These results demonstrate that aminoguanidine inhibits NO. production and suggest a role for NO. in the pathogenesis of diabetic vascular complications.

Amino Acid Oxidoreductases↗

PubMed1992

Does nitric oxide mediate autoimmune destruction of beta-cells? Possible therapeutic interventions in IDDM.

Cytokines have been implicated as immunological effector molecules that induce dysfunction and destruction of the pancreatic beta-cell. The mechanisms of cytokine action on the beta-cell are unknown; however, nitric oxide, resulting from cytokine-induced expression of nitric oxide synthase, has been implicated as the cellular effector molecule mediating beta-cell dysfunction. Nitric oxide is a free radical that targets intracellular iron-containing enzymes, which results in the loss of their function. The cytokine IL-1 beta induces the formation of nitric oxide in isolated rat islets and the insulinoma cell line, Rin-m5F. NMMA and NAME, both inhibitors of nitric oxide synthase, completely protect islets from the deleterious effects of IL-1 beta. These inhibitors are competitive in nature and inhibit both the cytokine-inducible and constitutive isoforms of nitric oxide synthase with nearly identical kinetics. This may preclude their use as therapeutic agents because of increases in blood pressure which result from the inhibition of constitutive nitric oxide synthase activity. Aminoguanidine, an inhibitor of nonenzymatic glycosylation of cellular and extracellular constituents associated with diabetic complications, recently has been reported to inhibit nitric oxide synthase. Aminoguanidine is approximately 40-fold more effective in inhibiting the inducible isoform of nitric oxide synthase, suggesting that aminoguanidine or analogues may serve as potential therapeutic agents to block diseases associated with nitric oxide production by the inducible isoform of nitric oxide synthase. In vivo administration of TNF IL-1 has been shown to induce anti-diabetogenic effects in the NOD mouse. This anti-diabetogenic effect of cytokines appears to conflict with evidence suggesting that cytokines mediate beta-cell dysfunction.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Oxidoreductases↗

PubMed1991

Interleukin-1 beta-induced formation of EPR-detectable iron-nitrosyl complexes in islets of Langerhans. Role of nitric oxide in interleukin-1 beta-induced inhibition of insulin secretion.

The molecular mechanism by which interleukin (IL)-1 inhibits insulin secretion and ultimately causes destruction of the pancreatic beta-cell remains unknown. Evidence is presented which suggests that IL-1 beta-induced inhibition of insulin secretion is dependent on the metabolism of L-arginine to nitric oxide. NG-Monomethylarginine, a competitive inhibitor of the L-arginine-dependent enzyme nitric oxide synthase, completely prevents IL-1-induced inhibition of glucose-stimulated insulin secretion as well as nitrite production by islets. It is further shown that IL-1 beta induces nitric oxide formation in islets as evidenced by an electron paramagnetic resonance feature at g = 2.04 which is similar to previously reported iron-nitrosyl complexes formed from the destruction of iron-sulfur centers by nitric oxide. Inhibition of the nitric oxide synthase by NG-monomethylarginine completely prevents the formation of this EPR signal in islets. These results show that IL-1-induced inhibition of insulin secretion is mediated through formation of nitric oxide and suggest that the generation of nitric oxide may represent the cellular mechanism responsible for beta-cell destruction.

Animals↗

PubMed1991

Biochemical basis for the specificity of alloxan inactivation of calmodulin-dependent protein kinase II.

The specificity and biochemical basis of inactivation of calmodulin-dependent protein kinase II by alloxan was studied in dispersed rat brain cells and a partially purified kinase preparation from an insulin-secreting tumor-cell line, RINm5f. When mechanically dispersed rat brain cells were incubated with [32P]-phosphate to label endogenous ATP, depolarization with 44 mM KCl produced a significant (P = 0.03) increase in phosphorylation of endogenous synapsin (132 +/- 8% of basal). Pre-treatment of the brain cells with 1.5 mM alloxan reduced depolarization-sensitive synapsin phosphorylation (109 +/- 5%). Phosphopeptide mapping of depolarization-phosphorylated synapsin showed that alloxan pre-treatment reduced phosphorylation specifically at synapsin sites phosphorylated by calmodulin-dependent protein kinase II. The results demonstrate selective inactivation of calmodulin-dependent protein kinase II activity by alloxan in an intact cell system, which may be useful in the study of the Type II kinase in cells and tissues. Using a partially purified kinase preparation from RINm5f cells, alloxan (100 microM) inactivated 76 +/- 1% calmodulin-dependent protein kinase II activity in 5 min at 37 degrees C. Subsequent incubation with dithiothreitol restored most of the activity. 5,5'-Dithiobis (2-nitrobenzoic acid) (I50 = 2.5 microM) also inactivated the kinase. These results suggested that a sulfhydryl group was involved at the inactivation site. Iodoacetamide (1.0 mM) had no inhibitory effect; however, preincubation with iodoacetamide protected the kinase activity from subsequent inactivation by alloxan. Covalent binding of [14C]-alloxan to calmodulin-dependent protein kinase was demonstrated.(ABSTRACT TRUNCATED AT 250 WORDS)

Alloxan↗

PubMed1990

Evidence for a role of microfilaments in insulin release from purified beta-cells.

To determine if the failure of purified beta-cells to secrete insulin in response to a glucose stimulus results from the absence of a cytoskeletal response, the effects of cytochalasins D and B on glucose-induced insulin release were investigated. Glucose alone failed to stimulate insulin release whereas glucose in the presence of glucagon, theophylline, cytochalasin D or B markedly potentiated insulin release. Cytochalasin D potentiated insulin secretion in a dose-dependent manner, and the combination of theophylline and cytochalasin D resulted in an insulin secretory response no greater than that produced by either agent alone. Both glucagon and theophylline are believed to mediate their effects via cAMP, however, cytochalasin D did not affect beta-cell cAMP levels. These results suggest that the inability of purified beta-cells to release insulin may result from the absence of the necessary modulation of the state of the microfilaments.

Actin Cytoskeleton↗

PubMed1990

Interleukin-1 induces rapid and transient expression of the c-fos proto-oncogene in isolated pancreatic islets and in purified beta-cells.

The effect of interleukin-1 beta (IL-1) on expression of c-fos mRNA in isolated rat pancreatic islets was examined. Accumulation of c-fos mRNA was demonstrable after 30 min of exposure to IL-1, peaked by 60 min, and declined thereafter. Fluorescence-activated cell sorting (FACS) of dispersed islet cells was employed to localize the accumulation of c-fos mRNA to the beta-cell. Cycloheximide did not influence the induction of c fos mRNA by IL-1. Accumulation of c-fos mRNA therefore appears to be an early signal transduction event in the beta-cell and a component of the cellular mechanism(s) by which IL-1 influences beta-cell function.

Animals↗

PubMed1990

Secretagogue-induced oscillations of cytoplasmic Ca2+ in single beta and alpha-cells obtained from pancreatic islets by fluorescence-activated cell sorting.

Pancreatic islet cells from normal adult rats were purified by autofluorescence-activated cell sorting (FACS). A purification of islet beta-cells (greater than 90%) and alpha-cells (greater than 70%) was obtained after FACS separation. Dual-wavelength microfluorimetry was employed for measurements of cytoplasmic Ca2+ concentration (Ca2+i) in single beta- and alpha-cells. In FACS-purified beta-cells, 11.8 mM glucose induced oscillations of Ca2+i with a frequency of 1 cycle per 2-4 min, whereas 20 mM glucose induced a rapid rise in Ca2+i followed by a sustained elevation in Ca2+i. In contrast, alpha-cells exhibited a decrease in Ca2+i following exposure to 20 mM glucose, and subsequent exposure to 20 mM arginine induced a large increase in Ca2+i with periodic fluctuations. FACS purification of a heterogeneous islet-cell population provides a unique model for characterizing secretagogue-induced changes in Ca2+i in single beta-and alpha-cells.

Animals↗

PubMed1990

Diacylglycerol synthesis de novo from glucose by pancreatic islets isolated from rats and humans.

Recent evidence has suggested that pancreatic islets isolated from rats synthesize 1,2-diacyl-sn-glycerol (DAG) de novo from glucose and that this process may constitute the long-sought link between the metabolism of glucose and the induction of insulin secretion. The cell-permeant diacylglycerol 1-oleoyl-2-acetyl-sn-glycerol (200 microM) has been found here to amplify both the first and second phases of insulin secretion from perifused human islets. Measurements of the mass of endogenous DAG in human pancreatic islets by enzymatic and by mass spectrometric methods indicate that levels of 200 microM may be achieved under physiologic conditions. Conversion of [14C]glucose to [14C]DAG has been demonstrated here to occur within 60 s of exposure of rat and human islets to stimulatory concentrations of glucose. This process has been found to be a quantitatively minor contributor to the total islet DAG mass after acute stimulation with glucose, however, and glucose has been found not to induce a rise in total islet DAG content within 20 min of induction of insulin secretion. In contrast to the case with rodent islets, two pharmacologic inhibitors of DAG-induced activation of protein kinase C (staurosporine and sphingosine) have been found not to influence glucose-induced insulin secretion from isolated human islets. These findings indicate that de novo synthesis of DAG from glucose does not participate in acute signal-response coupling in islets.

Alkaloids↗

PubMed1990

Interleukin 1 inhibits insulin secretion from isolated rat pancreatic islets by a process that requires gene transcription and mRNA translation.

Recombinant human IL 1 beta inhibits glucose-induced insulin secretion from isolated pancreatic islets and from purified beta-cells obtained by fluorescence-activated cell sorting (FACS) of dispersed islet cells. Brief (1 h) exposure of isolated islets to IL 1 produces sustained inhibition of insulin secretion for at least 17 h after the IL 1 has been removed from the culture medium. An inhibitory effect of IL 1 on insulin secretion is not observed when islets are coincubated with an inhibitor of DNA transcription (actinomycin D). This finding indicates that the inhibitory effect of IL 1 on insulin secretion requires transcription of one or more genes during the first hour of exposure of islets to IL 1. The inhibitory effect of IL 1 on insulin secretion also requires mRNA translation, because three structurally distinct inhibitors of protein synthesis (cycloheximide, anisomycin, and puromycin) prevent IL 1-induced inhibition of insulin secretion when added to islets after the 1-h exposure to IL 1. Two-dimensional gel electrophoresis of islet proteins metabolically labeled with [35S]methionine demonstrates that IL 1 augments the expression of a 65-kD (pl approximately 6.5) protein by greater than 2.5-fold. These findings indicate that biochemical events occurring within 1 h of exposure of islets to IL 1 lead to an inhibition of insulin secretion that persists for at least 17 h after the removal of IL 1. One of the early biochemical effects of IL 1 on islets is gene transcription (0-1 h), which is followed by mRNA translation (after 1 h). Our results suggest that the inhibitory effect of IL 1 on insulin secretion is mediated by protein(s) whose synthesis is induced by IL 1.

Animals↗

PubMed1989

Comparison of effects of phorbol esters and glucose on protein kinase C activation and insulin secretion in pancreatic islets.

The tumour-promoting phorbol ester 12-O-tetradecanoylphorbol 13-acetate (TPA) induces insulin secretion from isolated pancreatic islets, and this suggests a potential role for protein kinase C in the regulation of stimulus-secretion coupling in islets. In the present study, the hypothesis that the insulinotropic effect of TPA is mediated by activation of protein kinase C in pancreatic islets has been examined. TPA induced a gradual translocation of protein kinase C from the cytosol to a membrane-associated state which correlated with the gradual onset of insulin secretion. The pharmacologically inactive phorbol ester 4 alpha-phorbol 12,13-didecanoate did not mimic this effect. TPA also induced a rapid time-dependent decline of total protein kinase C activity in islets and the appearance of a Ca2+- and phospholipid-independent protein kinase activity. Insulin secretion induced by TPA was completely suppressed (IC50 approximately 10 nM) by staurosporine, a potent protein kinase C inhibitor. Staurosporine also inhibited islet cytosolic protein kinase C activity at similar concentrations (IC50 approximately 2 nM). In addition, staurosporine partially (approximately 60%) inhibited glucose-induced insulin secretion at concentrations (IC50 approximately 10 nM) similar to those required to inhibit TPA-induced insulin secretion, suggesting that staurosporine may act at a step common to both mechanisms, possibly the activation of protein kinase C. However, stimulatory concentrations of glucose did not induce down-regulation of translocation of protein kinase C, and the inhibition of glucose-induced insulin release by staurosporine was incomplete. Significant questions therefore remain unresolved as to the possible involvement of protein kinase C in glucose-induced insulin secretion.

Alkaloids↗

PubMed1989

Secretagogue-induced diacylglycerol accumulation in isolated pancreatic islets. Mass spectrometric characterization of the fatty acyl content indicates multiple mechanisms of generation.

Diacylglycerol accumulation has been examined in secretagogue-stimulated pancreatic islets with a newly developed negative ion chemical ionization mass spectrometric method. The muscarinic agonist carbachol induces islet accumulation of diacylglycerol rich in arachidonate and stearate, and a parallel accumulation of 3H-labeled diacylglycerol occurs in carbachol-stimulated islets that had been prelabeled with [3H]glycerol. Islets so labeled do not accumulate 3H-labeled diacylglycerol in response to D-glucose, but D-glucose does induce islet accumulation of diacylglycerol by mass. This material is rich in palmitate and oleate and contains much smaller amounts of arachidonate. Neither secretagogue influences triacylglycerol labeling, and neither induces release of [3H]choline or [3H]phosphocholine from islets prelabeled with [3H]choline. These observations indicate that the diacylglycerol that accumulates in islets in response to carbachol arises from hydrolysis of glycerolipids, probably including phosphoinositides. The bulk of the diacylglycerol which accumulates in response to glucose does not arise from glycerolipid hydrolysis and must therefore reflect de novo synthesis. The endogenous diacylglycerol which accumulates in secretagogue-stimulated islets may participate in insulin secretion because exogenous diacylglycerol induces insulin secretion from islets, and an inhibitor of diacylglycerol metabolism to phosphatidic acid augments glucose-induced insulin secretion.

Animals↗

PubMed1989

Interleukin-1 inhibits glucose-induced Ca2+ uptake by islets of Langerhans.

Recombinant interleukin-1 (rIL-1) is known to inhibit glucose-induced insulin secretion by islets of Langerhans, a novel target tissue of cytokine. We have investigated whether rIL-1 pretreatment affects biochemical mechanisms known to be involved in the regulation of Ca2+ homeostasis during glucose-induced insulin secretion. Glucose-induced Ca2+ uptake by intact islets through the plasma membrane was dramatically inhibited (96%) by rIL-1 (2 nM). rIL-1, however, did not affect Ca2+ uptake by, or Ins 1,4,5-P3-induced Ca2+ efflux from, the endoplasmic reticulum in digitonin-permeabilized islets, although glucose-induced accumulation of inositol trisphosphates was inhibited (38%). These results suggest that perturbation of intracellular Ca2+ homeostasis in islets is involved in inhibition of insulin secretion by rIL-1.

Animals↗

PubMed1989

Arachidonic acid metabolism in isolated pancreatic islets. V. The enantiomeric composition of 12-hydroxy-5,8,10,14-eicosatetraenoic acid indicates synthesis by a 12-lipoxygenase rather than a monooxygenase.

Recent evidence indicates that the arachidonate metabolite 12-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE) or its precursor may act as a second messenger in stimulus-response coupling in a variety of cells including Aplysia neurons, adrenal glomerulosa cells, and pancreatic islets. The compound 12(S)-HETE is generated from the precursor 12(S)-hydroperoxy-5,8,10,14-eicosatetraenoic acid (12(S)-HPETE), which is a product of the 12-lipoxygenase enzyme. Some cells have recently been found to produce the enantiomer 12(R)-HETE, apparently via a cytochrome P-450 monooxygenase, and the biologic actions of 12(R)-HETE and 12(S)-HETE differ. We have examined the stereochemistry of 12-HETE from isolated pancreatic islets both radiochemically and by a new mass spectrometric method capable of quantitating subnanogram amounts of 12-HETE stereoisomers. Endogenous 12-HETE from islets was found to be exclusively the S-isomer. D-Glucose stimulated both insulin secretion and islet accumulation of 12(S)-HETE but not of 12(R)-HETE. Pharmacologic inhibition of islet 12-HETE biosynthesis also suppressed glucose-induced insulin secretion. These findings suggest that islet 12-HETE is a product of a 12-lipoxygenase rather than of a cytochrome P-450 monooxygenase and further implicate 12-lipoxygenase products in stimulus-secretion coupling.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗

PubMed1989

Effects of sulfonamides on a metabolite-regulated ATPi-sensitive K+ channel in rat pancreatic B-cells.

Intracellular ATP (ATPi)-sensitive K+ [K+(ATP)] channels are now a recognized site of action of clinically useful hypoglycemic and hyperglycemic sulfonamides. We have further examined the action of these agents on single K+ channels in rat pancreatic B-cells 1) Tolbutamide and glyburide, two hypoglycemic sulfonylureas which decrease K+(ATP) channel activity in the cell-attached patch, affect the kinetics of K+(ATP) channel in a manner similar to glucose. They shorten the duration of the "burst," or cluster of open channel events, while lengthening the intervals between bursts. 2) The hyperglycemic vasodilator diazoxide increases mean K+(ATP) channel activity in the cell-attached patch as well as in the inside-out excised patch exposed to ATPi. It appears to lengthen channel bursts and shorten the intervals between them. Two structurally similar diuretics, hydrochlorothiazide and furosemide, which have mild hyperglycemic effects, do not increase K+(ATP) channel activity even at clinically toxic concentrations. 3) Neither the sulfonylureas nor diazoxide directly affect the activity of single delayed rectifier K+ channels or single calcium and voltage-activated K+ channels in normal B-cells.

Adenosine Triphosphate↗

PubMed1989

Interleukin 1-induced prostaglandin E2 accumulation by isolated pancreatic islets.

Recombinant human interleukin 1 alpha (IL-1) has been found to induce prostaglandin E2 (PGE2) accumulation by isolated rat islets of Langerhans at concentrations similar to those at which the cytokine inhibits glucose-induced insulin secretion and islet glucose oxidation. Maximal stimulation of PGE2 accumulation (5 times control value) occurred at 200 pM IL-1, and half-maximal stimulation occurred at 25 pM IL-1. Significant augmentation of PGE2 accumulation by IL-1 required 10-18 h of exposure to the cytokine. Islets that had been pretreated with IL-1 for 18 h showed elevated rates of PGE2 production at basal (3-mM) and stimulatory (16.5-mM) glucose concentrations and converted exogenous arachidonic acid to PGE2 at twice the maximal rate of control islets. Exogenous PGE2 did not mimic the inhibitory effects of IL-1 on glucose-induced insulin secretion or glucose oxidation. To rule out the possibility that endogenous PGE2 is involved in the inhibitory effects of IL-1, the effect of a cyclooxygenase inhibitor on IL-1-treated islets was examined. Pharmacological blockade of PGE2 biosynthesis by 10 microM indomethacin did not influence the inhibitory effects of IL-1 on glucose-induced insulin secretion or glucose oxidation. Thus, exogenous PGE2 does not mimic the effects of IL-1 on islets, and inhibition of endogenous PGE2 biosynthesis does not suppress the effects of IL-1 on islets. These results suggest that PGE2 is not a principal mediator of the inhibitory effects of IL-1 on glucose-induced insulin secretion or glucose oxidation.

Animals↗