Glucose-stimulated Insulin Secretion Response Research Articles

1745-P: Voltage-Gated K+ Channel Kv7.1 Is an Important Regulator of Insulin Secretion in Normal and Hyperinsulinemic Islets

Fifty percent of infants with Beckwith-Wiedemann syndrome (BWS), an overgrowth syndrome caused by genetic / epigenetic abnormalities in imprinted genes on chromosome 11p15, have persistent hypoglycemia due to hyperinsulinism (BWS-HI). BWS-HI islets exhibit increased baseline and glucose-stimulated insulin secretion (GSIS) and are responsive to the KATP channel inhibitor glyburide, suggesting it is not caused by impaired KATP channels. KCNQ1 expression, encoding the pore-forming α subunit of voltage-gated K+ channel Kv7.1, is reduced in BWS-HI islets compared to normal islets (3-fold; p = 4.5×10−7) and KCNQ1 loss-of-function mutations in humans are associated with HI. We used genetic and pharmacologic methods to modify Kv7.1 activity and examined changes to insulin secretion. In response to glucose, Kcnq1−/− mice had lower plasma glucose and higher plasma insulin than wild-type controls. Perifusion of Kcnq1−/− pancreatic islets with increasing concentrations of glucose showed that GSIS in these islets was faster and greater than in wild-type islets. The perifusion GSIS responses in normal human, wild-type mouse and Sur1−/− mouse (KATP-HI mouse model) islets with two different Kv7.1 activators (hexachlorophene or ML277) were markedly slower and diminished. In contrast, wild-type mouse islet perifusion with the Kv7.1 inhibitor chromanol 293B strikingly fastened and increased the GSIS response compared to vehicle controls. Membrane potential (Vm) analysis of Kcnq1−/− islets demonstrated that depolarization occurs more quickly during the initiation of insulin secretion compared to wild-type controls. Treatment with Kv7.1 activators resulted in Vm changes in both wild-type mouse and normal human islets compared to controls. Our results reveal the capacity of Kv7.1 to regulate insulin secretion in pancreatic islets and that Kv7.1 is a viable target for development of therapeutics for HI. Disclosure C.Juliana: Research Support; Crinetics Pharmaceuticals, Inc., Twist Bioscience, AmideBio. D.De leon: Consultant; Zealand Pharma A/S, Crinetics Pharmaceuticals, Inc., Eiger BioPharmaceuticals, Hanmi Pharm. Co., Ltd., Research Support; Ultragenix, Crinetics Pharmaceuticals, Inc., Hanmi Pharm. Co., Ltd., Rezolute, Inc. Funding National Institutes of Health (5R01DK098517-08)

Pseudoislet Aggregation of Pancreatic β-Cells Improves Glucose Stimulated Insulin Secretion by Altering Glucose Metabolism and Increasing ATP Production.

Appropriate glucose-stimulated insulin secretion (GSIS) by pancreatic β-cells is an essential component of blood glucose homeostasis. Configuration of β-cells as 3D pseudoislets (PI) improves the GSIS response compared to 2D monolayer (ML) culture. The aim of this study was to determine the underlying mechanisms. MIN6 β-cells were grown as ML or PI for 5 days. Human islets were isolated from patients without diabetes. Function was assessed by GSIS and metabolic capacity using the Seahorse bioanalyser. Connexin 36 was downregulated using inducible shRNA. Culturing MIN6 as PI improved GSIS. MIN6 PI showed higher glucose-stimulated oxygen consumption (OCR) and extracellular acidification (ECAR) rates. Further analysis showed the higher ECAR was, at least in part, a consequence of increased glycolysis. Intact human islets also showed glucose-stimulated increases in both OCR and ECAR rates, although the latter was smaller in magnitude compared to MIN6 PI. The higher rates of glucose-stimulated ATP production in MIN6 PI were consistent with increased enzyme activity of key glycolytic and TCA cycle enzymes. There was no impact of connexin 36 knockdown on GSIS or ATP production. Configuration of β-cells as PI improves GSIS by increasing the metabolic capacity of the cells, allowing higher ATP production in response to glucose.

Glycerol‐3‐phosphate phosphatase/ Pgp in Pancreatic ß‐cells Functions as a Glucose Excess Security Valve Preventing Oversecretion of Insulin Secretion and Glucotoxicity

Objective The recently identified enzyme in mammalian cells, glycerol-3-phosphate (Gro3P) phosphatase (G3PP), gene name Pgp, was proposed to regulate intermediary metabolism. G3PP was shown in in vitro studies to regulate metabolism and glucose stimulated insulin secretion (GSIS) in ß-cells. We now examined the in vivo role of G3PP in the control of insulin secretion and ß-cell glucotoxicity. Methods Glucose and insulin tolerance were studied in ß-cell specific G3PP-KO (BKO) mice. Body weight gain, fed glycemia and insulinemia were measured. Pancreatic islets were isolated for ex vivo GSIS and biochemical measurements. Results BKO mice show increased body weight gain, unaltered fed glycemia and insulinemia, and enhanced insulin secretion in response to glucose load in an intraperitoneal but not oral glucose tolerance test, reaching 21 and 14 mM glucose, respectively. Insulin sensitivity in vivo remains unchanged in the BKO mice. GSIS response ex vivo at 16 mM but not 8 mM glucose is higher in BKO mouse islets. BKO islets show reduced glucose-induced glycerol release and elevated O2 consumption and ATP production at high (16 mM) but not low (4 mM) glucose levels. Glucotoxicity at 30 mM glucose for 7 days led to increased apoptosis, reduced insulin content and expression of Pdx-1 and Ins-2 genes in BKO islets. Conclusion G3PP impacts insulin secretion in vivo and ex vivo only under conditions of high but not intermediate and low glucose levels. G3PP plays a role in preventing ß-cell glucotoxicity. These effect likely result from the capacity of G3PP to redirect the excess glucose carbons from intermediate metabolism to glycerol that exits ß-cells. We propose that G3PP acts as a glucose excess security valve to prevent excessive insulin secretion and ß-cell dysfunction when blood glucose reaches very high levels.

MEK/ERK Signaling in β-Cells Bifunctionally Regulates β-Cell Mass and Glucose-Stimulated Insulin Secretion Response to Maintain Glucose Homeostasis.

In diabetic pathology, insufficiency in β-cell mass, unable to meet peripheral insulin demand, and functional defects of individual β-cells in production of insulin are often concurrently observed, collectively causing hyperglycemia. Here we show that the phosphorylation of ERK1/2 is significantly decreased in the islets of db/db mice as well as in those of a cohort of subjects with type 2 diabetes. In mice with abrogation of ERK signaling in pancreatic β-cells through deletion of Mek1 and Mek2, glucose intolerance aggravates under high-fat diet-feeding conditions due to insufficient insulin production with lower β-cell proliferation and reduced β-cell mass, while in individual β-cells dampening of the number of insulin exocytosis events is observed, with the molecules involved in insulin exocytosis being less phosphorylated. These data reveal bifunctional roles for MEK/ERK signaling in β-cells for glucose homeostasis, i.e., in regulating β-cell mass as well as in controlling insulin exocytosis in individual β-cells, thus providing not only a novel perspective for the understanding of diabetes pathophysiology but also a potential clue for new drug development for diabetes treatment.

An increase in inflammation and islet dysfunction is a feature of prediabetes.

Type 2 diabetes (T2D) is a global health problem that will be diagnosed in almost 300 million people by 2025 according to the World Health Organization. Before being diagnosed with T2D, individuals may have glucose levels above normal but below the diabetic range. This condition is known as prediabetes. Studies showed that people with prediabetes had an increase in several pro-inflammatory cytokines in their serum and in their fasting glucose levels. The answer remains unclear when inflammation begins in the pancreas and islets, and what is the extent of this inflammation. Subjects with haemoglobin A1c levels from 5.7% to 6.4% were classified as pre-diabetic. Sections of pancreas and isolated islets from normal donors and donors with prediabetes were tested for markers of inflammation and glucose-stimulated insulin secretion (GSIS). Gene and protein expression of the inflammatory markers resistin, interleukin-1 beta, tumour necrosis factor-alpha, interleukin-6, and monocyte chemoattractant protein-1 increased in donors with prediabetes compared to normal donors. GSIS response was significantly decreased in pre-diabetic islets compared to normal islets. Donors with prediabetes also had decreased expression of CD163+ cells but not CD68+ cells. Based on our findings, inflammation and islet dysfunction may be more significant than originally thought in people with prediabetes. Rather than being in a normal state before diabetes occurs, it appears that subjects are already in an early diabetic condition resembling more closely T2D.

In vitro characterization of neonatal, juvenile, and adult porcine islet oxygen demand, β-cell function, and transcriptomes.

There is currently a shortage of human donor pancreata which limits the broad application of islet transplantation as a treatment for type 1 diabetes. Porcine islets have demonstrated potential as an alternative source, but a study evaluating islets from different donor ages under unified protocols has yet to be conducted. Neonatal porcine islets (NPI; 1-3days), juvenile porcine islets (JPI; 18-21days), and adult porcine islets (API; 2+years) were compared in vitro, including assessments of oxygen consumption rate, membrane integrity determined by FDA/PI staining, β-cell proliferation, dynamic glucose-stimulated insulin secretion, and RNA sequencing. Oxygen consumption rate normalized to DNA was not significantly different between ages. Membrane integrity was age dependent, and API had the highest percentage of intact cells. API also had the highest glucose-stimulated insulin secretion response during a dynamic insulin secretion assay and had 50-fold higher total insulin content compared to NPI and JPI. NPI and JPI had similar glucose responsiveness, β-cell percentage, and β-cell proliferation rate. Transcriptome analysis was consistent with physiological assessments. API transcriptomes were enriched for cellular metabolic and insulin secretory pathways, while NPI exhibited higher expression of genes associated with proliferation. The oxygen demand, membrane integrity, β-cell function and proliferation, and transcriptomes of islets from API, JPI, and NPI provide a comprehensive physiological comparison for future studies. These assessments will inform the optimal application of each age of porcine islet to expand the availability of islet transplantation.

GDF15 Is a Contraction-Induced Myokine That Regulates Pancreatic ß-Cell Function

β-cell dysfunction plays a major role in the onset of type 2 diabetes (T2D). Exercise improves or restores β-cell function in both humans and rodents with T2D. The specific mechanism is unclear. We hypothesized that exercise-induced myokines engage in cross-talk with the pancreas to help regulate β-cell function and mass. To test our hypothesis, differentiated C2C12 myotubes were subjected to electrical pulse stimulation (EPS) to simulate in vivo exercise. EPS-conditioned media from the contracting myotubes significantly elevated glucose-stimulated insulin secretion (GSIS) in β-cells vs. non-EPS control conditions (P<0.05). RNA-sequencing and bioinformatic analysis enabled us to identify Growth Differentiation Factor 15 (GDF15) as a novel contraction-induced myokine that potentially communicates with β-cells. At the cellular level, recombinant GDF15 protein treatment upregulated the GSIS response in β-cells by 55% (P<0.05), with no effect on cellular apoptosis, cytotoxicity or proliferation. Furthermore, qRT-PCR analysis, ELISA, immunoblots, and intracellular assays demonstrated that GDF15 may regulate first-phase insulin secretion by increasing the intracellular ATP/ADP ratio, inhibiting K+ channels and increasing the intracellular Ca2+ without affecting insulin synthesis. Using translational approaches, we found a positive correlation between fasting plasma GDF15 and insulin secretion in prediabetic subjects (R=0.64, P<0.01, n=22). A 6 week supervised functional high-intensity exercise intervention increased fasting plasma GDF15 by 35% in adults with T2D (P<0.01, n=12) and, interestingly, the increase in GDF15 was positively correlated with an increase in the β-cell disposition index (R=0.72, P<0.01, n=12), providing further support that GDF15 may be involved in improving β-cell function. In summary, these findings expand our understanding of skeletal muscle as an endocrine organ and identify GDF15 as a potential myokine for T2D therapy. Disclosure H. Zhang: None. A. Mulya: None. S. Nieuwoudt: None. R. McDowell: None. J.P. Kirwan: None.

FoxO1 inhibition promotes differentiation of human embryonic stem cells into insulin producing cells

Insulin-producing cells (IPCs) derived from human embryonic stem cells (hESCs) hold great potential for cell transplantation therapy in diabetes. Tremendous progress has been made in inducing differentiation of hESCs into IPCs in vitro, of which definitive endoderm (DE) protocol mimicking foetal pancreatic development has been widely used. However, immaturity of the obtained IPCs limits their further applications in treating diabetes. Forkhead box O1 (FoxO1) is involved in the differentiation and functional maintenance of murine pancreatic β cells, but its role in human β cell differentiation is under elucidation. Here, we showed that although FoxO1 expression level remained consistent, cytoplasmic phosphorylated FoxO1 protein level increased during IPC differentiation of hESCs induced by DE protocol. Lentiviral silencing of FoxO1 in pancreatic progenitors upregulated the levels of pancreatic islet differentiation-related genes and improved glucose-stimulated insulin secretion response in their progeny IPCs, whereas overexpression of FoxO1 showed the opposite effects. Notably, treatment with the FoxO1 inhibitor AS1842856 displayed similar effects with FoxO1 knockdown in pancreatic progenitors. These effects were closely associated with the mutually exclusive nucleocytoplasmic shuttling of FoxO1 and Pdx1 in the AS1842856-treated pancreatic progenitors. Our data demonstrated a promising effect of FoxO1 inhibition by the small molecule on gene expression profile during the differentiation, and in turn, on determining IPC maturation via modulating subcellular location of FoxO1 and Pdx1. Therefore, we identify a novel role of FoxO1 inhibition in promoting IPC differentiation of hESCs, which may provide clues for induction of mature β cells from hESCs and clinical applications in regenerative medicine.

Discovery, Synthesis, and Evaluation of 2,4-Diaminoquinazolines as a Novel Class of Pancreatic β-Cell-Protective Agents against Endoplasmic Reticulum (ER) Stress.

Pancreatic insulin-producing β-cell dysfunction and death plays central roles in the onset and progression of both type 1 and type 2 diabetes. Current antidiabetic drugs cannot halt the ongoing progression of β-cell dysfunction and death. In diabetes, a major cause for the decline in β-cell function and survival is endoplasmic reticulum (ER) stress. Here, we identified quinazoline derivatives as a novel class of β-cell protective agents against ER stress-induced dysfunction and death. A series of quinazoline derivatives were synthesized from dichloroquiazoline utilizing a sequence of nucleophilic reactions. Through SAR optimization, 2,4-diaminoquinazoline compound 9c markedly protects β-cells against ER stress-induced dysfunction and death with 80% maximum rescue activity and an EC50 value of 0.56 μM. Importantly, 9c restores the ER stress-impaired glucose-stimulated insulin secretion response and survival in primary human islet β-cells. We showed that 9c protects β-cells by alleviating ER stress through the suppression of the induction of key genes of the unfolded protein response and apoptosis.

The role of BH3-only protein Bmf in the pathogenesis of dominant negative hepatocyte nuclear factor-1 –induced mature-onset diabetes of the young in transgenic mice

Maturity Onset Diabetes of the Young 3 (MODY3) is the most common monogenic form of diabetes, characterized by early age of onset (before the age of 25), autosomal dominant transmission and severe defect in insulin secretion [1,2]. MODY accounts for 2-5% of Non-Insulin Dependent Diabetes Mellitus (NIDDM) cases, with MODY3 identified as the most common and severe form, accounting for 65% of all MODY cases and results from loss of function mutations of the transcription factor Hepatocyte Nuclear Factor-1 α (HNF1α). As a result of this, pancreatic islets show reduction in glucose-stimulated insulin secretion response and in beta cell mass, hallmarks of MODY3. Previous work in this laboratory has shown that induction of dominant negative mutant-HNF1a expression results in bioenergetic stress, activation of AMPK and induction of pro-apoptotic BH3-only family protein, Bmf [3].

DNA methylation directs functional maturation of pancreatic β cells.

Pancreatic β cells secrete insulin in response to postprandial increases in glucose levels to prevent hyperglycemia and inhibit insulin secretion under fasting conditions to protect against hypoglycemia. β cells lack this functional capability at birth and acquire glucose-stimulated insulin secretion (GSIS) during neonatal life. Here, we have shown that during postnatal life, the de novo DNA methyltransferase DNMT3A initiates a metabolic program by repressing key genes, thereby enabling the coupling of insulin secretion to glucose levels. In a murine model, β cell-specific deletion of Dnmt3a prevented the metabolic switch, resulting in loss of GSIS. DNMT3A bound to the promoters of the genes encoding hexokinase 1 (HK1) and lactate dehydrogenase A (LDHA) - both of which regulate the metabolic switch - and knockdown of these two key DNMT3A targets restored the GSIS response in islets from animals with β cell-specific Dnmt3a deletion. Furthermore, DNA methylation-mediated repression of glucose-secretion decoupling genes to modulate GSIS was conserved in human β cells. Together, our results reveal a role for DNA methylation to direct the acquisition of pancreatic β cell function.

TCF7L2 and Glucose Metabolism: Time to Look Beyond the Pancreas

Noncoding genetic variation in the locus encoding for the Wnt signaling effector TCF7L2 remains the strongest genetic determinant of type 2 diabetes (T2D) risk in humans. This association raises the hypothesis that disease variants alter the quantitative, spatial, and/or temporal expression patterns of this gene. Understanding the mechanisms by which TCF7L2 and Wnt signaling regulate glucose metabolism may reveal novel insights into the pathogenesis of T2D, as well as highlight cellular and genetic pathways amenable to becoming novel therapeutic targets. Therefore, a large body of work has emerged over the past 4 years describing previously unknown glucose metabolism roles of TCF7L2. Curiously, most of this work has focused on TCF7L2 actions in pancreatic β-cells, despite evidence that canonical Wnt signaling is not active in adult β-cells (1). The extensive evaluation of TCF7L2 actions or Wnt signaling effects in β-cells have resulted in contradictory findings at the molecular (2,3), cellular (1,4), and whole-animal physiology levels (5–7). Particularly difficult to reconcile is the incongruence of data showing that the presumed diabetogenic effects of TCF7L2 in β-cells, such as a blunted glucose-stimulated insulin secretion response, arises from reducing TCF7L2 expression (3,8). In contrast, evidence from human genetics and genomics studies suggests the risk alleles associated with T2D lead to increased expression of TCF7L2 (2,9–11), a notion recently confirmed by mouse models harboring germline null alleles …

Prolactin Receptors Are Critical to the Adaptation of Islets to Pregnancy

During pregnancy there is an enhanced need for insulin to accommodate the growing fetal compartment as well as the substantial increase in insulin resistance. Failure of the islets to adapt to this increased demand for insulin leads to gestational diabetes. The report by Huang et al. (1), using an in vivo model of prolactin (PRL) receptor deficiency, provides an important validation of the hypothesis that -cell PRL receptors are central to mechanisms whereby islets adapt to pregnancy (Fig. 1). This study showed not only that PRL receptor deficiency leads to gestational diabetes, but the genetic phenotype of the mother influences the outcome of islet development in the fetus. That islets undergo changes during pregnancy was observed as early as 1930 (2), when Cramer concluded that islets are a very plastic tissue that undergo considerable changes, especially during pregnancy. The changes he observed included increased secretory activity, islet growth, and neogenesis. Direct evidence for functional changes in islets did not occur until the development of a sensitive insulin assay in the 1960s, when it was reported that there was a progressive increase in both fasting and glucosestimulated insulin secretion throughout the course of human pregnancy (3). This and subsequent research led to the characterization of pregnancy as a condition of elevated serum insulin levels, slightly lower blood glucose levels, and peripheral insulin resistance. The short-term regulation of insulin secretion is achieved by elevating blood glucose. However, if this were the only mechanism available for increasing insulin secretion during pregnancy, there would be a need for persistent hyperglycemia, a condition detrimental both to the mother and the developing fetus. Thus, when there is an increased need for insulin over a prolonged period of time, such as occurs in pregnancy, islets must undergo adaptive changes. The outcome of the up-regulation must be such that there is enhanced insulin secretion at normal glucose levels. There are three basic mechanisms whereby one can increase insulin secretion at normal glucose concentrations: increase the islet -cell mass, increase the sensitivity of insulin secretion in response to glucose, or both. Evidence that there is an increase islet/ -cell mass comes from a number of studies (4–7). These studies indicate that there is an approximate 2-fold increase in islet mass. DNA content per islet also indicates an increase in islet mass, and both morphometric and DNA to protein ratio methods indicate -cell hypertrophy as well as -cell hyperplasia (8– 12). Evidence for increased -cell mitosis comes from tritiated thymidine and bromodeoxyuridine labeling of islets during pregnancy (4, 13, 14). Overall, these reports indicate that islet mass doubles, and the increase is a consequence of new -cell formation as well as an increase in -cell size. There is less information on whether islet neogenesis occurs during pregnancy. One report failed to detect evidence for islet neogenesis during pregnancy but did show that another condition of persistent hyperlactogenemia may result in islet neogenesis (15). There is also evidence for an increase in glucose-sensitive insulin secretion. During rodent pregnancy, fasting serum insulin levels are increased, and glucose levels are decreased (8, 16, 17), similar to that observed in human pregnancy. Green and Taylor (9) showed a leftward shift of the glucose-stimulated insulin secretion response curve in islets isolated from pregnant rats. In a similar study, we used perfused pancreas preparations to examine insulin secretion throughout rat pregnancy. A leftward shift in glucose-responsive insulin secretion as well as above-threshold insulin release was first noted on d 10 and peaked by d 15 (4). The threshold for glucose-stimulated insulin secretion decreased from 5.7–3.3 mM by d 15 pregnancy. The lowering of the threshold for glucose-stimulated insulin secretion is a key feature of islets as they adapt to pregnancy. It is through this maneuver that a large increase in insulin secretion can be achieved at fasting blood glucose levels, as is seen during pregnancy. The most important changes in islet adaptation to pregnancy are enhanced insulin secretion and enhanced -cell mass. Candidate hormones must be shown to induce these changes. Although a variety of hormones increase during pregnancy, only PRL and placental lactogen, which acts through PRL receptors, are capable of inducing the changes that occur in islets during

Programming of defective rat pancreatic beta-cell function in offspring from mothers fed a low-protein diet during gestation and the suckling periods.

Poor fetal and infant nutrition has been linked to impaired glucose tolerance in later life. We studied the effect of protein deficiency during gestation and the suckling period in a rat model and found that poor nutrition 'programmes' pancreatic beta-cell GK (glucokinase; known as the glucose sensor) and glucose-stimulated insulin secretion response in newborn, suckling and adult rat offspring. Pregnant female rats were divided into three groups: a control group was kept on a normal protein (20%) diet, another group was fed a low-protein (LP) (6%) diet during gestation and suckling periods (LP-G + S group) and another was fed a LP diet during gestation then a normal protein diet during the suckling period (LP-G group). The pulsatile glucose-stimulated insulin secretion response was acutely disrupted and the peak insulin secretion was markedly decreased in newborn and 3-week-old offspring of the LP-G + S group compared with the control group. Also, there was an altered pulsatile secretory response in adults of the LP-G + S and 3-week-old and adult offspring of the LP-G groups compared with the control group. GK protein levels, detected by Western blotting, were decreased in newborn and 3-week-old offspring of both LP-G + S and LP-G groups compared with the control groups. The Km and Vmax of GK were altered. The prenatal and postnatal LP diet appeared to have a permanent effect in increasing the affinity of GK for glucose (indicated by decreased Km values) and decreasing the Vmax. This showed that the critical period of programming of the function of GK was after birth and during the postnatal weaning period, since the adult offspring of the LP-G + S group when fed a normal protein diet showed no reversal in the Km values of the enzyme. Similar experiments in adult offspring of the LP-G group showed normalization of the Km values of GK at 3 weeks of age. In conclusion, fetal and infantile nutrition 'programmes' pancreatic beta-cell function; poor nutrition during this period caused irreversible effects on glucose homoeostatic mechanisms in the offspring, which may predispose the offspring to diabetes in later life.

GLUT-2 gene transfer into insulinoma cells confers both low and high affinity glucose-stimulated insulin release. Relationship to glucokinase activity

The rat insulinoma cell line RIN 1046-38 loses glucose-stimulated insulin secretion as a function of time in culture. We found that the loss of glucose sensing in these cells was correlated with the loss of expression of GLUT-2 and glucokinase. Stable transfection of RIN cells with a plasmid containing the GLUT-2 cDNA conferred glucose-stimulated insulin release in intermediate but not high passage cells, with the near-maximal 3-fold increase occurring at 50 microM glucose. GLUT-2 expressing cells also exhibited a larger response to the combination of 5 mM glucose + 1 microM forskolin than untransfected cells (7.9 versus 1.6-2.7-fold, respectively). GLUT-2 expressing intermediate passage, but not high passage, RIN cells exhibited a 4-fold increase in glucokinase enzymatic activity relative to nonexpressing controls. Glucokinase activity was also increased by transfer of the GLUT-2 gene into intermediate passage RIN cells via recombinant adenovirus. Preincubation of GLUT-2 expressing intermediate passage RIN cells with 2-deoxyglucose to inhibit low Km hexokinases resulted in a glucose-stimulated insulin secretion response that was shifted toward the physiologic range. These studies indicate that GLUT-2 expression confers both a high and low affinity glucose-stimulated insulin secretion response to intermediate passage RIN cells.