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Query: UMLS:C0011849 (diabetes)
 277,896 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Intracellular production of nitric oxide (NO) is thought to mediate the pancreatic B-cell-directed cytotoxicity of cytokines in insulin-dependent diabetes mellitus, and recent evidence has indicated that this may involve induction of apoptosis. A primary effect of NO is to activate soluble guanylyl cyclase leading to increased cGMP levels and this effect has been demonstrated in pancreatic B-cells, although no intracellular function has been defined for islet cGMP. Here we demonstrate that the NO donor, GSNO, induces apoptosis in the pancreatic B-cell line HIT-T15 in a dose- and time-dependent manner. This response was significantly attenuated by micromolar concentrations of a specific inhibitor of soluble guanylyl cyclase, ODQ, and both 8-bromo cGMP (100 microM) and dibutyryl cGMP (300 microM) were able to fully relieve this inhibition. In addition, incubation of HIT-T15 cells with each cGMP analogue directly promoted cell death in the absence of ODQ. KT5823, a potent and highly selective inhibitor of cGMP-dependent protein kinase (PKG), abolished the induction of cell death in HIT cells in response to either GSNO or cGMP analogues. This effect was dose-dependent over the concentration range of 10-250 nM. Overall, these data provide evidence that the activation of apoptosis in HIT-T15 cells by NO donors is secondary to a rise in cGMP and suggest that the pathway controlling cell death involves activation of PKG.
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PMID:Evidence for the involvement of cGMP and protein kinase G in nitric oxide-induced apoptosis in the pancreatic B-cell line, HIT-T15. 900 15

We have previously shown that diabetes is associated with a decrease in Na(+)-H+ exchange activity in rat cardiac papillary muscle. The present work has been carried out in order to elucidate the factors responsible for such an alteration. Thus, we have studied the effects of pH0 and intracellular Ca2+ on Na(+)-H+ exchange in ventricular myocytes isolated from streptozotocin-induced diabetic rat hearts. pH1 was recorded using carboxy-seminaphthorhodafluor (SNARF-1). The NH4+ (10 mmol/L) prepulse method was used to induce an acid load in order to activate Na(+)-H+ exchange in HEPES-buffered Tyrode's solution. Whereas diabetes did not change intracellular buffering power, it significantly decreased acid efflux through Na(+)-H+ exchange (acid efflux, 4.32 +/- 0.4 [n = 32, normal cells] versus 2.5 +/- 0.2 [n = 43, diabetic cells] meq/L per minute at pHi 6.9; P < .02). Upon changes of pH0 (at a range of 8.0 to 6.8), acid efflux similarly varied in normal and diabetic cells, thus pointing to an unchanged pH0 sensitivity of Na(+)-H+ exchange. Buffering of intracellular Ca2+ by pretreatment of the cells with BAPTA-AM (25 mumol/L Ca2(+)-chelator) resulted in a decrease by approximately 58% of acid efflux in the diabetic group. This decrease was even more marked in normal cells (by approximately 74%). Interestingly, the pH1 dependence of the acid efflux carried by Na(+)-H+ exchange then became identical in both groups of cells, thus pointing to a role for intracellular Ca2+ in the diabetes-related alterations of the exchange. Inhibition of calmodulin (by 1.5 mumol/L calmidazolium) and of Ca2+/calmodulin-dependent protein kinase II (by 2 mumol/L 1-[N,O-bis(5-isoquinolinesulfonyl)-N-methyl-L-tyrosyl]-4-phenylpiperazin e [KN-62]) significantly slowed down pH1 recovery in both normal and diabetic cells. However, the effect of KN-62 was significantly lower in diabetic cells (efflux decreased by approximately 17%) compared with normal cells (decrease by 45%). In conclusion, these data, in light of recent observations showing a decreased [Ca2+]i associated with diabetes in isolated ventricular myocytes, suggest that changes in intracellular Ca2+ may play an important role in altering Na(+)-H+ exchange activity in diabetic ventricular myocytes. They also point to diabetes-related alterations in the Ca2+/calmodulin protein kinase II-dependent phosphorylation of Na(+)-H+ exchange.
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PMID:Modulation by pH0 and intracellular Ca2+ of Na(+)-H+ exchange in diabetic rat isolated ventricular myocytes. 901 47

The metabolism of the storage polysaccharide glycogen is intimately linked with insulin action and blood glucose homeostasis. Insulin activates both glucose transport and glycogen synthase in skeletal muscle. The central issue of a long-standing debate is which of these two effects determines the rate of glycogen synthesis in response to insulin. Recent studies with transgenic animals indicate that, under appropriate conditions, each process can contribute to determining the extent of glycogen accumulation. Insulin causes stable activation of glycogen synthase by promoting dephosphorylation of multiple sites in the enzyme. A model linking this action to the mitogen-activated protein kinase signaling pathway via the phosphorylation of the regulatory subunit of glycogen synthase phosphatase gained widespread acceptance. However, the most recent evidence argues strongly against this mechanism. A newer model, in which insulin inactivates the enzyme glycogen synthase kinase-3 via the protein kinase B pathway, has emerged. Though promising, this model still does not completely explain the molecular basis for the insulin-mediated activation of glycogen synthase, which remains one of the many unknowns of insulin action.
Diabetes 1997 Apr
PMID:New insights into the role and mechanism of glycogen synthase activation by insulin. 907 92

The mechanisms by which glucose-dependent insulinotropic polypeptide (GIP) stimulates insulin secretion were investigated by measurements of whole-cell Ca2+ currents, the cytoplasmic Ca2+ concentration, and cell capacitance as an indicator of exocytosis in individual mouse pancreatic beta-cells maintained in short-term culture. GIP produced a 4.2-fold potentiation of depolarization-induced exocytosis. This stimulation of exocytosis was not associated with a change in the whole-cell Ca2+-current, and there was only a small increase (30%) in the cytoplasmic Ca2+ concentration [intercellular free Ca2+([Ca2+]i)]. The stimulatory effect of GIP on exocytosis was blocked by pretreatment with the specific protein kinase A (PKA) inhibitor Rp-8-Br-cAMPS. Glucagon-like peptide-I(7-36) amide (GLP-I) stimulated exocytosis (90%) in the presence of a maximal GIP concentration (100 nmol/l). Replacement of GLP-I with forskolin produced a similar stimulatory action on exocytosis. These effects of GLP-I and forskolin in the presence of GIP did not involve a change in the whole-cell Ca2+-current or [Ca2+]i. GIP was ineffective in the presence of both forskolin and the phosphodiesterase inhibitor isobutylmethylxanthine (IBMX). Under the same experimental conditions, the protein kinase C (PKC)-activating phorbol ester 4-phorbol 12-myristate 13-acetate (PMA) stimulated exocytosis (60%). Collectively, our data indicate that the insulinotropic hormone GIP stimulates insulin secretion from pancreatic beta-cells, through the cAMP/PKA signaling pathway, by interacting with the secretory machinery at a level distal to an elevation in [Ca2+]i.
Diabetes 1997 Apr
PMID:Protein kinase A-dependent stimulation of exocytosis in mouse pancreatic beta-cells by glucose-dependent insulinotropic polypeptide. 907 1

Culture of mesangial cells (MCs) in 5.6 vs. 30.0 mmol/l glucose for 3 weeks induced a sustained increase in protein kinase C (PKC) activity, transforming growth factor (TGF)-beta1 mRNA, bioactive TGF-beta, and collagen synthesis. Nitric oxide (NO), generated exogenously by the NO donor S-nitroso-N-acetyl, D,L-penicillamine (SNAP) or endogenously after the exposure of MC to interleukin-1beta (IL-1beta), suppressed bioactive TGF-beta in MCs cultured in 5.6 or 30.0 mmol/l glucose and suppressed or abolished increases in TGF-beta1 mRNA and collagen synthesis induced by high concentrations of glucose or phorbol 12,13-dibutyrate without altering values obtained with normal glucose concentrations. SNAP had a transient suppressive effect on PKC activity, which may explain at least in part some of the actions of SNAP. The selective inhibitor of PKC, bisindolylmaleimide (GFX), mimicked NO action. The ability of SNAP and IL-1beta to suppress TGF-beta and collagen synthesis was not mediated by cGMP, since the cGMP analog, 8-Br-PET-cGMP, did not mimic NO action and an antagonist of cGMP-dependent protein kinase, Rp-8-pCPT-cGMPs, did not prevent the inhibitory actions of SNAP. N-omega-L-arginine methyl ester (NMMA) increased TGF-beta in glomerular capillary endothelial cells (GCECs) and stimulated collagen synthesis by MC in a co-culture with GCECs. Captopril inhibited TGF-beta and collagen synthesis and increased cGMP in co-cultures of GCECs and MCs. These effects of captopril were abolished by NMMA, implying mediation by NO. Thus, endogenous NO produced by GCECs may modulate TGF-beta production by both GCECs and MCs and act to suppress matrix protein synthesis by MCs.
Diabetes 1997 Apr
PMID:Nitric oxide inhibition of transforming growth factor-beta and collagen synthesis in mesangial cells. 907 10

Leptin is an adipocyte hormone involved in the regulation of energy homeostasis. Generally accepted biological effects of leptin are inhibition of food intake and stimulation of metabolic rate in ob/ob mice that are defective in the leptin gene. In contrast to these centrally mediated effects of leptin, we are reporting here on leptin effects on isolated rat adipocytes. Leptin impairs several metabolic actions of insulin, i.e. stimulation of glucose transport, glycogen synthase, lipogenesis, inhibition of isoproterenol-induced lipolysis, and protein kinase A activation, as well as stimulation of protein synthesis. Insulin effects were reduced by leptin (2 nM) with a half-life of about 8 h. At low leptin concentrations (<1 nM), the insulin sensitivity was reduced leading to a shift to the right in the dose-response curve. At higher concentrations the responsiveness was diminished, resulting in nearly complete inhibition of insulin effects at >30 nM leptin. The IC50 value of leptin was 3.1 +/- 1 nM after 15 h of preincubation of adipocytes in primary culture. The natural splice variant des-Gln49-leptin exhibited a significantly lower potency. Adipocytes regained full insulin sensitivity within a few hours after leptin removal. The stimulation of glucose transport by vanadate was not affected by leptin. These data show specific and potent impairment of insulin action by leptin in the physiological concentration range of both leptin and insulin, which may be related to the pathophysiology of insulin resistance in both non-insulin-dependent diabetes mellitus and obesity.
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PMID:Leptin impairs metabolic actions of insulin in isolated rat adipocytes. 909 5

Mitogen-activated protein (MAP) kinase plays crucial roles in cell growth and differentiation. It has recently been shown that the MAP kinase cascade in growth factor signaling diverges and cross-talks with other signaling pathways. In the present study, we examined the effects of wortmannin, a specific inhibitor of phosphatidylinositol 3-kinase (PI3-kinase), on the activation of Ras, Raf-1 kinase, and MAP kinase by insulin and epidermal growth factor (EGF). The effect of LY294002, a structurally distinct PI3-kinase inhibitor, on the activation of Raf-1 kinase by both ligands was also examined. In 3T3-L1 adipocytes, 25 nmol/l wortmannin inhibited the insulin-induced activation of Raf-1 kinase to the basal level, whereas the same dose of wortmannin had little effect on the EGF-induced activation of Raf-1 kinase. One hundred micromol/l LY294002 blocked insulin-induced activation of Raf-1 kinase without affecting EGF-induced activation of this kinase. Twenty-five nmol/l wortmannin inhibited the insulin-induced activation of MAP kinase to the basal level with no effect on the EGF-induced activation of this kinase. But the same dose of wortmannin did not affect the formation of guanosine 5'-triphosphate (GTP)-bound Ras stimulated by either ligand. In KB cells, results similar to those in 3T3-L1 adipocytes were obtained. In contrast, in Chinese hamster ovary cells overexpressing the human insulin receptor (CHO-HIR cells), neither wortmannin nor LY294002 inhibited the insulin-induced activation of Raf-1 kinase, and wortmannin had little effect on the activation of MAP kinase by insulin. These results indicate that 1) PI3-kinase or wortmannin-sensitive molecules are involved in the interaction between activated Ras and Raf-1 kinase in the insulin signaling in 3T3-L1 adipocytes, 2) the involvement of PI3-kinase or wortmannin-sensitive molecules in the insulin-induced activation of MAP kinase appears to be cell-type specific, and 3) differential mechanisms to activate Raf-1 kinase and MAP kinase by insulin and EGF exist.
Diabetes 1997 May
PMID:Differential activation of mitogen-activated protein kinase by insulin and epidermal growth factor in 3T3-L1 adipocytes: a possible involvement of PI3-kinase in the activation of the MAP kinase by insulin. 913 38

High-resolution capacitance measurements were used to explore the effects of the gut hormones GLP-I(7-36) amide [glucagon-like peptide I(7-36) amide] and GIP (glucose-dependent insulinotropic polypeptide) on Ca2+-dependent exocytosis in glucagon-secreting rat pancreatic alpha-cells. Both peptides produced a greater than threefold potentiation of secretion evoked by voltage-clamp depolarizations, an effect that was associated with an approximately 35% increase of the Ca2+ current. The stimulatory actions of GLP-I(7-36) amide and GIP were mimicked by forskolin and antagonized by the protein kinase A (PKA)-inhibitor Rp-8-Br-cAMPS. The islet hormone somatostatin inhibited the stimulatory action of GLP-I(7-36) amide and GIP via a cyclic AMP-independent mechanism, whereas insulin had no effect on exocytosis. These data suggest that the alpha-cells are equipped with receptors for GLP-I and GIP and that these peptides, in addition to their well-established insulinotropic capacity, also stimulate glucagon secretion. We propose that the reported inhibitory action of GLP-I on glucagon secretion is accounted for by a paracrine mechanism (e.g., mediated by stimulated release of somatostatin that in turn suppresses exocytosis in the alpha-cell).
Diabetes 1997 May
PMID:Glucagon-like peptide I and glucose-dependent insulinotropic polypeptide stimulate Ca2+-induced secretion in rat alpha-cells by a protein kinase A-mediated mechanism. 913 46

Activation of glycogen synthesis in skeletal muscle in response to insulin results from the combined inactivation of glycogen synthase kinase-3 (GSK-3) and activation of the protein phosphatase-1, changing the ratio between the inactive phosphorylated state of the glycogen synthase to the active dephosphorylated state. In a search for genetic defects responsible for the decreased insulin stimulated glycogen synthesis seen in patients with non-insulin-dependent diabetes mellitus (NIDDM) and their glucose-tolerant first-degree relatives we have performed mutational analysis of the coding region of the 2 isoforms of GSK-3alpha and GSK-3beta in 72 NIDDM patients and 12 control subjects. No structural changes were detected apart from a few silent mutations. Mapping of the GSK-3alpha to chromosome 19q13.1-13.2 and the GSK-3beta to chromosome 3q13.3-q21 outside known genetic loci linked to NIDDM further makes it unlikely that these genes are involved in the pathogenesis of common forms of NIDDM.
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PMID:Chromosomal mapping and mutational analysis of the coding region of the glycogen synthase kinase-3alpha and beta isoforms in patients with NIDDM. 926 89

Carbachol can stimulate insulin release in RINm5F cells by a mechanism that does not involve the elevation of cytosolic free Ca2+ concentrations or the activation of conventional protein kinase Cs (Mol Pharmacol 47:863-870, 1995). Thus, a novel signal transduction pathway links the muscarinic activation of the cells to increased insulin secretion. The question arises as to whether the pathway results from a novel receptor, different from the five established muscarinic receptors, or whether a "normal" receptor in the RINm5F cell activates a novel pathway. To distinguish between these two possibilities, the muscarinic receptors in the RINm5F cell were identified. Using polymerase chain reaction, combined with subcloning and DNA sequencing techniques, the cDNAs that encode the established M3 and M4 receptors were identified. The cDNAs for the Ml, M2, and M5 receptors were not found. Pharmacological studies showed a rank order of potency for muscarinic receptor subtype antagonists to inhibit carbachol-induced insulin release (half-maximal inhibitory concentration [pIC50] values given in parentheses): atropine (nonselective, 9.0) > 4-diphenyl-acetoxy-N-methyl piperidine methiodide (M3/M1, 8.6) > para-fluoro-hexahydrosiladiphenidol (M3, 8.1) > hexahydrosiladiphenidol (M3, 8.0) > tropicamide (M4, 6.4) > pirenzepine (M1, 6.1) > methoctramine (M2, 5.9). This antagonist profile suggests that it is the M3 receptor that mediates carbachol-induced insulin release. In this case, the novel signaling involved in the unusual carbachol response would not be due to a novel receptor but to the well-characterized M3 receptor. It appears, therefore, that the novel portion of the signaling pathway lies downstream of the M3 receptor and may consist of products of phosphatidylinositol hydrolysis, other than inositol triphosphate and diacylglycerol, resulting from the activation of phospholipase C. While a contributory role of the M4 receptor cannot be ruled out, there is no evidence in its favor other than its presence in the cell.
Diabetes 1997 Sep
PMID:Identification of muscarinic receptor subtypes in RINm5F cells by means of polymerase chain reaction, subcloning, and DNA sequencing. 928 41


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