Oral administration of osteocalcin improves glucose utilization by stimulating glucagon-like peptide-1 secretion

Uncarboxylated osteocalcin (GluOC), a bone-derived hormone, regulates energy metabolism by stimulating insulin secretion and pancreatic β-cell proliferation. We previously showed that the effect of GluOC on insulin secretion is mediated largely by glucagon-like peptide-1 (GLP-1) secreted from the intestine in response to GluOC exposure. We have now examined the effect of oral administration of GluOC on glucose utilization as well as the fate of such administered GluOC in mice. Long-term intermittent or daily oral administration of GluOC reduced the fasting blood glucose level and improved glucose tolerance in mice without affecting insulin sensitivity. It also increased the fasting serum insulin concentration as well as the β-cell area in the pancreas. A small proportion of orally administered GluOC reached the small intestine and remained there for at least 24 h. GluOC also entered the general circulation, and the serum GLP-1 concentration was increased in association with the presence of GluOC in the intestine and systemic circulation. The putative GluOC receptor, GPRC6A was detected in intestinal cells, and was colocalized with GLP-1 in some of these cells. Our results suggest that orally administered GluOC improved glucose handling likely by acting from both the intestinal lumen and the general circulation, with this effect being mediated in part by stimulation of GLP-1 secretion. Oral administration of GluOC warrants further study as a safe and convenient option for the treatment or prevention of metabolic disorders.     

瞬时感受器电位香草酸受体1与疼痛治疗

背景 疼痛是临床上常见却又难以达到满意治疗效果的综合征.以往的镇痛药物主要致力于阻断疼痛刺激向大 脑传递,而非针对疼痛产生的根源,即介导疼痛的受体.目前随着疼痛刺激性受体的识别与克隆,疼痛治疗领域得以新的发展.目的 总结近期国内外对瞬时感受器电位香草酸受体1(transient receptor potential v...     

Protein engineering strategies for sustained glucagon-like peptide-1 receptor-dependent control of glucose homeostasis

OBJECTIVE—We have developed a novel platform for display and delivery of bioactive peptides that links the biological properties of the peptide to the pharmacokinetic properties of an antibody. Peptides engineered in the MIMETIBODY platform have improved biochemical and biophysical properties that are quite distinct from those of Fc-fusion proteins. CNTO736 is a glucagon-like peptide 1 (GLP-1) receptor agonist engineered in our MIMETIBODY platform. It retains many activities of native GLP-1 yet has a significantly enhanced pharmacokinetic profile. Our goal was to develop a long-acting GLP-1 receptor agonist with sustained efficacy.RESEARCH DESIGN AND METHODS—In vitro and in vivo activity of CNTO736 was evaluated using a variety of rodent cell lines and diabetic animal models.RESULTS—Acute pharmacodynamic studies in diabetic rodents demonstrate that CNTO736 reduces fasting and postprandial glucose, decreases gastric emptying, and inhibits food intake in a GLP-1 receptor–specific manner. Reduction of food intake following CNTO736 dosing is coincident with detection of the molecule in the circumventricular organs of the brain and activation of c-fos in regions protected by the blood-brain barrier. Diabetic rodents dosed chronically with CNTO736 have lower fasting and postprandial glucose and reduced body weight.CONCLUSIONS—Taken together, our data demonstrate that CNTO736 produces a spectrum of GLP-1 receptor–dependent actions while exhibiting significantly improved pharmacokinetics relative to the native GLP-1 peptide.Drug development strategies for therapeutic peptides continue to be challenging despite advances in technologies such as pegylation and lipidation (1–4). Although important biological processes are regulated by peptides, successful development of peptide drugs has been limited and transformation of a metabolically labile peptide into a drug remains challenging. In contrast, considerable advances have been made in the development of antibody therapeutics (5,6). A technology that could link the activity of a target peptide with the pharmacokinetic characteristics of an antibody would be a valuable addition to tools available for drug discovery. To address this need, we developed the MIMETIBODY platform as a novel technology for the display and delivery of bioactive peptides. Using protein design tools, we linked an antibody Fc domain to a bioactive glucagon-like peptide 1 (GLP-1) analog and engineered the construct for optimal biochemical and biophysical properties.GLP-1 is a 30–amino acid peptide secreted from L-cells of the intestine following nutrient ingestion (7–10). GLP-1 is rapidly degraded in vivo with a half-life of <2 min and cleared via the kidney (11,12). When circulating glucose concentrations are elevated, GLP-1 increases insulin and decreases glucagon secretion from the pancreas and slows gastric emptying, thereby reducing glucose appearance in the circulation and enhancing glucose clearance from the circulation (13–15). In rodent models, GLP-1 expands β-cell mass via induction of β-cell proliferation and neogenesis and reduction of β-cell apoptosis (16–20). The cytoprotective actions of GLP-1 also promote survival of human islets (21,22). Furthermore, GLP-1 reduces food intake, and therapy with GLP-1 receptor agonists has been associated with weight loss in clinical studies (23,24). Thus, GLP-1 receptor agonists are attractive therapeutic candidates for the treatment of type 2 diabetes.CNTO736 is a GLP-1 receptor agonist engineered in our MIMETIBODY platform that incorporates a GLP-1 peptide analogue genetically fused to a domain that includes the Fc portion of an antibody (25,26). In addition to an amino acid substitution in the peptide rendering it resistant to dipeptidyl peptidase IV (27,28), the increased molecular weight and pharmacokinetic properties of an Fc were expected to enable sustained delivery of a GLP-1 receptor agonist. We demonstrate that CNTO736 dose-dependently increases cAMP and insulin secretion from islets in a glucose-dependent manner. In rodent models of type 2 diabetes, acute dosing with CNTO736 lowers fasting and postprandial blood glucose with a significantly longer duration of action than native GLP-1, and chronic dosing with CNTO736 decreases body weight. Although CNTO736 is a large molecule that is not likely to efficiently cross the blood-brain barrier, it can be detected in the circumventricular organs of the brain following peripheral dosing, and c-fos expression is detected in regions that are protected by the blood-brain barrier. Food intake is reduced in mice and rats following peripheral dosing with CNTO736, correlating with the appearance of the molecule in the hypothalamus. Hence, the generation of stable bioactive peptide therapeutics with optimized pharmacokinetic properties may provide a new option for the treatment of metabolic disorders.     

Distinct effects of glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1 on insulin secretion and gut motility

Glucose-induced insulin secretion from pancreatic beta-cells depends critically on ATP-sensitive K(+) channel (K(ATP) channel) activity, but it is not known whether K(ATP) channels are involved in the potentiation of insulin secretion by glucose-dependent insulinotropic polypeptide (GIP). In mice lacking K(ATP) channels (Kir6.2(-/-) mice), we found that pretreatment with GIP in vivo failed to blunt the rise in blood glucose levels after oral glucose load. In Kir6.2(-/-) mice, potentiation of insulin secretion by GIP in vivo was markedly attenuated, indicating that K(ATP) channels are essential in the insulinotropic effect of GIP. In contrast, pretreatment with glucagon-like peptide-1 (GLP-1) in Kir6.2(-/-) mice potentiated insulin secretion and blunted the rise in blood glucose levels. We also found that GLP-1 inhibited gut motility whereas GIP did not. Perfusion experiments of Kir6.2(-/-) mice revealed severely impaired potentiation of insulin secretion by 1 nmol/l GIP and substantial potentiation by 1 nmol/l GLP-1. Although both GIP and GLP-1 increase the intracellular cAMP concentration and potentiate insulin secretion, these results demonstrate that the GLP-1 and GIP signaling pathways involve the K(ATP) channel differently.     

瞬时感受器电位香草酸受体1与局部麻醉药物神经毒性

背景 瞬时感受器电位香草酸受体1 (transient receptor potential vanilloid 1,TRPV1)是一种非选择性阳离子通道,主要分布于感觉神经纤维,介导伤害性感受的传入.同时,它能够将外来刺激进行整合影响神经递质的释放以及激活细胞内蛋白酶,从而调节突触传递和细胞功能(如细胞凋亡).局部麻醉药物可以激活TRPV1,且在高浓度时具有神经毒性,表现为病理性疼痛和痛觉过敏,可能与神经细胞的损伤有关.目的 综述TRPV1受体在局部麻醉药物外周神经毒性中的作用机制的研究进展.内容 TRPV1受体的活化能够升高神经纤维局部麻醉药物的浓度而增加其阻断效能,同时增加细胞内钙离子浓度,释放谷氨酸及激活N-甲基-D-天冬氨酸受体(N-methyl-D-aspartate receptor,NMDAR),最终通过钙超载、氧化应激损伤及细胞凋亡途径的活化导致神经元凋亡,介导局部麻醉药物物神经毒性反应.趋向 鉴于TRPV1受体在局部麻醉药物神经毒性的发生机制中所起的作用,靶向调节TRPV1受体的功能是否可以防治局部麻醉药物的神经毒性值得研究.     

Transient receptor potential vanilloid 1 antagonist, capsazepine, improves survival in a rat hemorrhagic shock model

OBJECTIVE: To evaluate the role of transient receptor potential vanilloid 1 (TRPV1) in a rat hemorrhagic shock (HS) model using the TRPV1 antagonist, capsazepine (CPZ). SUMMARY BACKGROUND DATA: TRPV1, distributed within the sensory nerve, plays a role in the regulation of cardiovascular functions. TRPV1 may be involved in the cardiovascular responses to HS. METHODS: Male rats were anesthetized and HS was induced with the mean arterial pressure (MAP) at 30 mm Hg for 90 minutes. CPZ (5.0 micromol/kg) was administered at 30 minutes after the shock induction, and the 24-hour survival rates were assessed. The MAP, heart rate, and shed blood volume (SBV) were recorded throughout the experiment. Arterial blood gas analysis and the plasma catecholamines levels were measured before and after HS. Double-immunohistochemistry for Fos and tyrosine hydroxylase (TH) was performed in the rostral ventrolateral medulla (RVLM) of the brain. RESULTS: CPZ significantly improved the 24-hour survival rates, which was accompanied by the increase in the MAP and the SBV, a decrease of the plasma catecholamines levels, and attenuation of the severe metabolic acidosis. Furthermore, CPZ reduced the percentage of double-labeled neurons for Fos and TH in the RVLM of the rat brain. CONCLUSIONS: TRPV1 may be involved in the regulation of the cardiovascular responses to HS, at least in part, by recruiting catecholaminergic neurons in the RVLM. CPZ appears to induce metabolic compensations, which may be potentially useful in HS.     

Short-chain fatty acids stimulate glucagon-like peptide-1 secretion via the G-protein-coupled receptor FFAR2

Interest in how the gut microbiome can influence the metabolic state of the host has recently heightened. One postulated link is bacterial fermentation of "indigestible" prebiotics to short-chain fatty acids (SCFAs), which in turn modulate the release of gut hormones controlling insulin release and appetite. We show here that SCFAs trigger secretion of the incretin hormone glucagon-like peptide (GLP)-1 from mixed colonic cultures in vitro. Quantitative PCR revealed enriched expression of the SCFA receptors ffar2 (grp43) and ffar3 (gpr41) in GLP-1-secreting L cells, and consistent with the reported coupling of GPR43 to Gq signaling pathways, SCFAs raised cytosolic Ca2+ in L cells in primary culture. Mice lacking ffar2 or ffar3 exhibited reduced SCFA-triggered GLP-1 secretion in vitro and in vivo and a parallel impairment of glucose tolerance. These results highlight SCFAs and their receptors as potential targets for the treatment of diabetes.     

胰高血糖素样肽1受体激动剂的肾脏保护作用

糖尿病肾病(DKD)是糖尿病最常见的微血管并发症之一,其发病机制复杂,治疗手段有限,寻找新的方法防治DKD已成为当今研究的重要方向。有研究发现,胰高血糖素样肽1受体激动剂(GLP-1RAs)具有不依赖于血糖的肾脏保护作用,可预防蛋白尿的发生,可能有助于延缓2型糖尿病患者估算肾小球滤过率(eGFR)的下降。本文就GLP-1RAs的肾脏保护机制及临床证据进行综述。     

Transient receptor potential vanilloid receptor subtype 1 in painful bladder syndrome and its correlation with pain

PURPOSE: Painful bladder syndrome is a chronic, debilitating bladder hypersensitivity disorder characterized by urinary frequency, urgency and bladder pain without an identifiable cause. Recent advances in understanding the molecular basis of hypersensitivity provide an opportunity to advance the understanding of and treatment for painful bladder syndrome. We studied the heat and capsaicin receptor transient receptor potential vanilloid receptor subtype 1 in the bladder in patients with painful bladder syndrome and their relationship to pain symptoms. MATERIALS AND METHODS: Bladder biopsies were obtained from 20 characterized subjects with painful bladder syndrome and 25 with asymptomatic microscopic hematuria as controls. Specimens were immunostained using specific antibodies to transient receptor potential vanilloid receptor subtype 1 and neurofilaments as a structural maker. Nerve fiber and urothelial staining were quantified with computerized image analysis. The results of immunohistochemistry were correlated with the pain score. RESULTS: There was a marked increase in suburothelial nerve fibers expressing transient receptor potential vanilloid receptor subtype 1 in painful bladder syndrome in comparison with that in controls (p <0.0001). The ratio of transient receptor potential vanilloid receptor subtype 1 fibers to neurofilaments was also significantly increased in painful bladder syndrome, suggesting over expression of transient receptor potential vanilloid receptor subtype 1 (p <0.0001). When all specimens studied were included, the pain score correlated significantly with the relative nerve fiber density of transient receptor potential vanilloid receptor subtype 1 in the suburothelium (r = 0.6862, p = 0.0002) as well as the ratio of transient receptor potential vanilloid receptor subtype 1 fibers to neurofilaments (r = 0.5554, p = 0.004). Urothelial transient receptor potential vanilloid receptor subtype 1 showed a tendency toward an increase in the painful bladder syndrome group but it did not achieve statistical significance. No correlation was found between transient receptor potential vanilloid receptor subtype 1 immunoreactivity of urothelium or neurofilament fibers and the pain score. CONCLUSIONS: This study shows increased transient receptor potential vanilloid receptor subtype 1 in nerve fibers of the bladder in painful bladder syndrome and a correlation of the pain score with the relative density of transient receptor potential vanilloid receptor subtype 1 nerve fibers. Transient receptor potential vanilloid receptor subtype 1 may have a role in the pathophysiology of painful bladder syndrome and it is a potential target for novel therapeutic agents.     

Role of leptin in the regulation of glucagon-like peptide-1 secretion

Glucagon-like peptide-1 (GLP-1), released from intestinal endocrine L cells, is a potent insulinotropic hormone. GLP-1 secretion is diminished in obese patients. Because obesity is linked to abnormal leptin signaling, we hypothesized that leptin may modulate GLP-1 secretion. Leptin significantly stimulated GLP-1 secretion (by up to 250% of control) from fetal rat intestinal cells, a mouse L cell line (GLUTag), and a human L cell line (NCI-H716) in a dose-dependent manner (P < 0.05-0.001). The long form of the leptin receptor was shown to be expressed, and leptin induced the phosphorylation of STAT3 in the three cell types. The leptin receptor was also expressed by rodent and human intestinal L cells, and leptin (1 mg/kg i.p.) significantly stimulated GLP-1 secretion in rats and ob/ob mice. To determine the effect of leptin resistance on GLP-1 secretion, C57BL/6 mice were fed a high-fat (45%) or low-fat (10%) diet for 8 weeks. Mice on the high-fat diet became obese; developed glucose intolerance, hyperinsulinemia, and hyperleptinemia; and were leptin resistant. Mice on the high-fat diet also had twofold lower basal plasma GLP-1 and a diminished GLP-1 response to oral glucose, by 28.5 +/- 5.0% (P < 0.05). These results show for the first time that leptin stimulates GLP-1 secretion from rodent and human intestinal L cells, and they suggest that leptin resistance may account for the decreased levels of GLP-1 found in obese humans.     

Effects of glucagon-like peptide-1 receptor agonists on renal function

Glucagon-like peptide-1 (GLP-1) receptor agonists result in greater improvements in glycemic control than placebo and promote weight loss with minimal hypoglycemia in patients with type 2 diabetes mellitus. A number of case reports show an association of GLP-1 receptor agonists, mainly exenatide, with the development of acute kidney injury. The present review aims to present the available data regarding the effects of GLP-1 receptor agonists on renal function, their use in subjects with chronic renal failure and their possible association with acute kidney injury. Based on the current evidence, exenatide is eliminated by renal mechanisms and should not be given in patients with severe renal impairment or end stage renal disease. Liraglutide is not eliminated by renal or hepatic mechanisms, but it should be used with caution since there are only limited data in patients with renal or hepatic impairment. There is evidence from animal studies that GLP-1 receptor agonists exert protective role in diabetic nephropathy with mechanisms that seem to be independent of their glucose-lowering effect. Additionally, there is evidence that GLP-1 receptor agonists influence water and electrolyte balance. These effects may represent new ways to improve or even prevent diabetic nephropathy.     

Protein kinase Czeta activation mediates glucagon-like peptide-1-induced pancreatic beta-cell proliferation

Glucagon-like peptide-1 (GLP-1), an insulinotropic and glucoincretin hormone, is a potentially important therapeutic agent in the treatment of diabetes. We previously provided evidence that GLP-1 induces pancreatic beta-cell growth nonadditively with glucose in a phosphatidylinositol-3 kinase (PI-3K)-dependent manner. In the present study, we investigated the downstream effectors of PI-3K to determine the precise signal transduction pathways that mediate the action of GLP-1 on beta-cell proliferation. GLP-1 increased extracellular signal-related kinase 1/2, p38 mitogen-activated protein kinase (MAPK), and protein kinase B activities nonadditively with glucose in pancreatic beta(INS 832/13) cells. GLP-1 also caused nuclear translocation of the atypical protein kinase C (aPKC) zeta isoform in INS as well as in dissociated normal rat beta-cells as shown by immunolocalization and Western immunoblotting analysis. Tritiated thymidine incorporation measurements showed that the p38 MAPK inhibitor SB203580 suppressed GLP-1-induced beta-cell proliferation. Further investigation was performed using isoform-specific pseudosubstrates of classical (alpha, beta, and gamma) or zeta aPKC isoforms. The PKCzeta pseudosubstrate suppressed the proliferative action of GLP-1, whereas the inhibitor of classical PKC isoforms had no effect. Overexpression of a kinase-dead PKCzeta acting as a dominant negative protein suppressed GLP-1-induced proliferation. In addition, ectopic expression of a constitutively active PKCzeta mutant stimulated tritiated thymidine incorporation to the same extent as GLP-1, and the glucoincretin had no growth-promoting action under this condition. The data indicate that GLP-1-induced activation of PKCzeta is implicated in the beta-cell proliferative signal of the insulinotropic hormone. The results are consistent with a model in which GLP-1-induced PI-3K activation results in PKCzeta translocation to the nucleus, which may play a role in the pleiotropic effects (DNA synthesis, metabolic enzymes, and insulin gene expression) of the glucoincretin.     

Leptin regulation of the anorexic response to glucagon-like peptide-1 receptor stimulation

Leptin reduces food intake in part by enhancing satiety responses to gastrointestinal signals produced in response to food consumption. Glucagon-like peptide 1 (GLP-1), secreted by the intestine when nutrients enter the gut, is one such putative satiety signal. To investigate whether leptin enhances the anorexic effects of GLP-1, rats received either saline or a subthreshold dose of leptin before intraperitoneal injection of either GLP-1 or Exendin-4 (Ex4; a GLP-1 receptor agonist). Leptin pretreatment strongly enhanced anorexia and weight loss induced by GLP-1 or Ex4 over 24 h. Conversely, fasting attenuated the anorexic response to GLP-1 or Ex4 treatment via a leptin-dependent mechanism, as demonstrated by our finding that the effect of fasting was reversed by physiological leptin replacement. As expected, Ex4 induced expression of c-Fos protein, a marker of neuronal activation, in hindbrain areas that process afferent input from satiety signals, including the nucleus of the solitary tract and area postrema. Unexpectedly, leptin pretreatment blocked this response. These findings identify physiological variation of plasma leptin levels as a potent regulator of GLP-1 receptor-mediated food intake suppression and suggest that the underlying mechanism is distinct from that which mediates interactions between leptin and other satiety signals.     

Arcuate glucagon-like peptide 1 receptors regulate glucose homeostasis but not food intake

OBJECTIVE—Glucagon-like peptide-1 (GLP-1) promotes glucose homeostasis through regulation of islet hormone secretion, as well as hepatic and gastric function. Because GLP-1 is also synthesized in the brain, where it regulates food intake, we hypothesized that the central GLP-1 system regulates glucose tolerance as well.RESEARCH DESIGN AND METHODS—We used glucose tolerance tests and hyperinsulinemic-euglycemic clamps to assess the role of the central GLP-1 system on glucose tolerance, insulin secretion, and hepatic and peripheral insulin sensitivity. Finally, in situ hybridization was used to examine colocalization of GLP-1 receptors with neuropeptide tyrosine and pro-opiomelanocortin neurons.RESULTS—We found that central, but not peripheral, administration of low doses of a GLP-1 receptor antagonist caused relative hyperglycemia during a glucose tolerance test, suggesting that activation of central GLP-1 receptors regulates key processes involved in the maintenance of glucose homeostasis. Central administration of GLP-1 augmented glucose-stimulated insulin secretion, and direct administration of GLP-1 into the arcuate, but not the paraventricular, nucleus of the hypothalamus reduced hepatic glucose production. Consistent with a role for GLP-1 receptors in the arcuate, GLP-1 receptor mRNA was found to be expressed in 68.1% of arcuate neurons that expressed pro-opiomelanocortin mRNA but was not significantly coexpressed with neuropeptide tyrosine.CONCLUSIONS—These data suggest that the arcuate GLP-1 receptors are a key component of the GLP-1 system for improving glucose homeostasis by regulating both insulin secretion and glucose production.The importance of gastrointestinal hormones signaling gut absorption of carbohydrates and downstream processes involved in glucose disposal has received increasing attention. Prominent among these is glucagon-like peptide-1 (GLP-1), which is produced by L-cells of the ileum and is secreted during meal ingestion. GLP-1 augments nutrient-induced insulin release (1,2), inhibits glucagon release (3), slows gastric emptying (4), and has islet-independent effects to reduce hepatic glucose production (5–8). Studies in animals and humans have demonstrated that GLP-1 signaling is necessary for normal glucose tolerance (9). Moreover, two newly approved therapies for type 2 diabetic patients act through GLP-1 signaling to improve glucose homeostasis.Most of the evidence demonstrating a role for GLP-1 in glucose homeostasis has focused on actions within the pancreatic islet. However, GLP-1 is also synthesized in a discrete population of neurons in the hindbrain (10–12), and GLP-1 receptors are highly expressed in various regions of the hypothalamus (13) including the arcuate nucleus (ARC) and the paraventricular nucleus (PVN) (14), two areas where immunoreactive GLP-1 fibers terminate (11). Central nervous system (CNS) GLP-1 receptors have been linked to the control of food intake, endocrine and behavioral responses to stress, and visceral illness (15–17). Although there is evidence that circulating GLP-1 agonists can activate CNS neurons (18) and that GLP-1 may cross the blood-brain barrier (19), central and peripheral GLP-1 signaling systems are generally held to be separate.Compelling recent evidence links a number of CNS systems to the regulation of peripheral glucose levels. While hypothalamic areas such as the PVN and the dorsal medial and the ventromedial hypothalamus may play a role in glucose homeostasis during stress (20–22), there is strong evidence that the ARC plays a key role in maintaining normal glucose levels in response to anorectic peptides or nutrients by regulation of glucose production (23–26). Given this emerging evidence for CNS involvement in the regulation of peripheral metabolism and the broad role that peripheral GLP-1 signaling plays in regulating glucose homeostasis, we hypothesized that CNS GLP-1 receptors would have multiple coordinated effects to improve glucose tolerance. Specifically, we focused on the ARC because GLP-1 receptors are found in this region, and previous studies have shown that neurons in this area regulate glucose production. Thus, a second hypothesis was that ARC GLP-1 receptors regulate glucose output. Finally, using dual in situ hybridization histochemistry, we evaluated ARC GLP-1 receptor expression on orexigenic neuropeptide tyrosine (NPY) and anorexigenic proopiomelanocortin (POMC) neurons.     

A novel glucose-sensing mechanism contributing to glucagon-like peptide-1 secretion from the GLUTag cell line

Glucagon-like peptide 1 (GLP-1) secretion from intestinal L-cells is triggered by luminal nutrients. We reported previously that glucose-triggered GLP-1 release from the L-cell model GLUTag involves closure of ATP-sensitive K+ (K(ATP)) channels. We show here that GLP-1 secretion and electrical activity of GLUTag cells is triggered not only by metabolizable sugars (glucose or fructose) but also by the nonmetabolizable monosaccharide methyl-alpha-glucopyranoside. Responses to glucose and methyl-alpha-glucopyranoside were impaired by the sodium-glucose cotransporter (SGLT) inhibitor phloridzin. SLGT1 and 3 were detected in GLUTag cells by RT-PCR. Whereas fructose closed K(ATP) channels, methyl-alpha-glucopyranoside increased the membrane conductance and generated an inward current. Low concentrations of glucose and methyl-alpha-glucopyranoside also triggered small inward currents and enhanced the action potential frequency. We conclude that whereas low concentrations of metabolizable sugars trigger GLP-1 secretion via K(ATP) channel closure, SGLT substrates generate small inward currents as a result of the electrogenic action of the transporter. This transporter-associated current can trigger electrical activity and secretion when the concentration of substrate is high or when outward currents are reduced by metabolic closure of the K(ATP) channels. Electrogenic sugar entry via SGLTs provides a novel mechanism for glucose sensing by neuroendocrine cells.