Pain Control, Glucose Control, and Quality of Life in Patients With Chronic Pancreatitis After Total Pancreatectomy With Islet Autotransplantation: A Preliminary Report.

BACKGROUND: Total pancreatectomy (TP) is offered as a last treatment option for pain relief in patients with chronic pancreatitis. Concurrent islets autotransplantation (TP-IAT) may improve glucose control. METHODS: We analyzed results in 20 recent patients who underwent TP-IAT at The University of Chicago. The median observation period was 28 months (2-38). Data were collected prospectively then analyzed retrospectively. RESULTS: The number of patients requiring opioids daily for pain control decreased from 16 (80%) prior to surgery to 2 (13%) 1 year after, with only 1 (6.5%) patient experiencing persistent phantom pancreatic pain. Opioid requirements decreased from a median 56.3 (0-240) morphine equivalent dose to 5 (0-130) on day 75 and to 0 (0-30) at 1-year follow up. Five patients (25%) completely stopped insulin support prior to day 75 while maintaining hemoglobin A1c of 5.9% (5-6.3). Eight (53%) patients were insulin free at 1 year with A1c of 6% (5.5-6.8) and a similar rate persisted in next 2 years. For the remaining patients, the more islet function that was preserved, the less insulin they required and A1c was closer to optimal. Quality of Life (QoL) measured by SF36 Physical (PCS) and Mental (MCS) Component Score improved on day 75 (P < .001) and maintained improvement later on. Both PCS and MCS improved regardless of whether patient requires insulin support or not. CONCLUSIONS: Improvements of QoL with pain resolution and good glucose control can be achieved after TP-IAT in properly selected patients with CP and intractable pain, regardless of patient insulin support status.

External Validation of the Newly Developed BETA-2 Scoring System for Pancreatic Islet Graft Function Assessment.

BACKGROUND: BETA-2 score using a single fasting blood sample was developed to estimate beta-cell function after islet transplantation (ITx) and was validated internally by a high ITx volume center (Edmonton). The goal was to validate BETA-2 externally, in our center. METHODS: Areas under receiver operating characteristic curves (AUROCs) were obtained to see if beta score or BETA-2 would better detect insulin independence and glucose intolerance. RESULTS: We analyzed values from 48 mixed meal tolerance tests (MMTTs) in 4 ITx recipients with a long-term follow-up to 140 months (LT group) and from 54 MMTTs in 13 short-term group patients (ST group). AUROC for no need for insulin support was 0.776 (95% confidence interval [CI] 0.539-1, P = .02) and 0.922 (95% CI 0.848-0.996, P < .001) for beta score and 0.79 (95% CI 0.596-0.983, P = .003) and 0.941 (95% CI 0.86-1, P < .001) for BETA-2, in LT and ST groups, respectively, and did not differ significantly. In LT group BETA-2 score ≥ 13.03 predicted no need for insulin supplementation with sensitivity of 98%, specificity of 50%, positive predictive value (PPV) of 93%, and negative predictive value (NPV) of 75%. In ST group the optimal cutoff was ≥13.63 with sensitivity of 92% and specificity, PPV, and NPV 82% to 95%. For the detection of glucose intolerance BETA-2 cutoffs were <19.43 in LT group and <17.23 in ST group with sensitivity > 76% and specificity, PPV, and NPV > 80% in both groups. CONCLUSION: BETA-2 score was successfully validated externally and is a practical tool allowing for frequent and reliable assessments of islet graft function based on a single fasting blood sample.

Patients with KCNJ11-related diabetes frequently have neuropsychological impairments compared with sibling controls.

AIMS: KCNJ11-related diabetes is the most common form of permanent neonatal diabetes and has been associated with a spectrum of neurodevelopmental problems. We compared neurodevelopmental outcomes in patients with KCNJ11 mutations and their sibling controls. METHODS: Through our Monogenic Diabetes Registry (http://monogenicdiabetes.uchicago.edu/), we evaluated 23 patients with KCNJ11 mutations with (n = 9) and without (n = 14) global developmental delay successfully treated with sulfonylurea and 20 healthy sibling controls, using a battery of targeted neuropsychological and behavioural assessments with scaled scores that are comparable across a wide range of ages. RESULTS: Patients with KCNJ11-related diabetes without global developmental delay had significant differences compared with sibling controls on a range of assessments including IQ, measures of academic achievement and executive function. KCNJ11 patients with global delay exhibited significant differences in behavioural symptoms with a tendency to avoid social contact and displayed a reduced ability to adapt to new circumstances. Parents reported more immature behaviour, gross mood swings, bizarre thoughts, other unusual and severe behaviours, and there were also significant deficits in all subdomains of daily living skills. CONCLUSIONS: This series represents the largest and most comprehensive study of neuropsychological and behavioural dysfunction of individuals with KCNJ11 diabetes and is the first to compare outcome with sibling controls. Our data demonstrate the variety of neurodevelopmental problems seen in those with KCNJ11 mutations, even in those without recognized global developmental delays. These data can be used to counsel families and guide structured neurodevelopmental assessments and treatments based on the initial genetic diagnosis in patients with neonatal diabetes.

Resting beta-cells - A functional reserve?

Pancreatic beta-cells play a pivotal role to synthesize and secrete insulin, as the solo source of the body. Physical as well as functional loss of beta-cells over a certain threshold result in diabetes. While the mechanisms underlying beta-cell loss in various types of diabetes have been extensively studied, less is known about residual beta-cells, found even in autoimmune type 1 diabetes and type 2 diabetes with a substantial amount. Why have these beta-cells been spared? Some patients with neonatal diabetes have demonstrated the life-changing restoration of functional beta-cells that were inactive for decades but awakened in several weeks following specific treatment. The recent striking outcomes of bariatric surgery in many obese diabetic patients indicate that their beta-cells are likely "preserved" rather than irreversibly lost even in the multifactorial polygenic state that is type 2 diabetes. Collectively, the preservation of residual beta-cells in various diabetic conditions challenges us regarding our understanding of beta-cell death and survival, where their sustenance may stem from the existence of resting beta-cells under physiological conditions. We posit that beta-cells rest and that studies of this normal feature of beta-cells could lead to new approaches for potentially reactivating and preserving beta-cell mass in order to treat diabetes.

Ion channels and regulation of insulin secretion in human ß-cells: a computational systems analysis.

In mammals an increase in glucose leads to block of ATP dependent potassium channels in pancreatic ß cells leading to membrane depolarization. This leads to the repetitive firing of action potentials that increases calcium influx and triggers insulin granule exocytosis. Several important differences between species in this process suggest that a dedicated human-oriented approach is advantageous as extrapolating from rodent data may be misleading in several respects. We examined depolarization-induced spike activity in pancreatic human islet-attached ß-cells employing whole-cell patch-clamp methods. We also reviewed the literature concerning regulation of insulin secretion by channel activity and constructed a data-based computer model of human ß cell function. The model couples the Hodgkin-Huxley-type ionic equations to the equations describing intracellular Ca²âº homeostasis and insulin release. On the basis of this model we employed computational simulations to better understand the behavior of action potentials, calcium handling and insulin secretion in human ß cells under a wide range of experimental conditions. This computational system approach provides a framework to analyze the mechanisms of human ß cell insulin secretion.

Genome wide association studies for diabetes: perspective on results and challenges.

Recent results of genome wide association study (GWAS) for diabetes genes, while reaching impressive technical milestones and implicating new findings for research, have been uniformly disappointing in terms of immediate clinical utility. The relative risk associated with any of the newly reported genetic loci, or even considering all of them together, is far less than simply that which can be obtained by taking a history and a physical exam. For type 2 diabetes (T2D), GWAS have implicated novel pathways, supported previously known associations, and highlighted the importance of the beta cell and insulin secretion. Monogenic forms of diabetes, on the other hand, continue to yield interesting insights into genes controlling human beta cell function but most cases of monogenic diabetes are simply not diagnosed. Here, we briefly review recent results related to type 1, type 2 and maturity onset diabetes of youth (MODY) diabetes and suggest that future studies emphasizing quantitative traits are likely to yield even more insights.

Bursting and calcium oscillations in pancreatic beta-cells: specific pacemakers for specific mechanisms.

Oscillatory phenomenon in electrical activity and cytoplasmic calcium concentration in response to glucose are intimately connected to multiple key aspects of pancreatic ß-cell physiology. However, there is no single model for oscillatory mechanisms in these cells. We set out to identify possible pacemaker candidates for burst activity and cytoplasmic Ca(2+) oscillations in these cells by analyzing published hypotheses, their corresponding mathematical models, and relevant experimental data. We found that although no single pacemaker can account for the variety of oscillatory phenomena in ß-cells, at least several separate mechanisms can underlie specific kinds of oscillations. According to our analysis, slowly activating Ca(2+)-sensitive K(+) channels can be responsible for very fast Ca(2+) oscillations; changes in the ATP/ADP ratio and in the endoplasmic reticulum calcium concentration can be pacemakers for both fast bursts and cytoplasmic calcium oscillations, and cyclical cytoplasmic Na(+) changes may underlie patterning of slow calcium oscillations. However, these mechanisms still lack direct confirmation, and their potential interactions raises new issues. Further studies supported by improved mathematical models are necessary to understand oscillatory phenomena in ß-cell physiology.

A brief perspective on insulin production.

The preeminent role of the beta cell is to manufacture, store and release insulin. The mature insulin molecule is composed of two polypeptide chains designated as A and B that are joined by two pairs of disulfide bonds with an additional intramolecular disulfide bond in the A chain. However, the two chains of the insulin molecule are not synthesized as separate polypeptide chains but rather are generated by specific proteolytic processing of a larger precursor, proinsulin. This discovery in 1967 and the concept of prohormones changed our view of the biosynthesis of hormones and neuropeptides. It allowed studies of the regulation of insulin biosynthesis that highlighted the key role of glucose. In addition, the C-peptide, the polypeptide that joins the A and B chains in proinsulin and is stored with insulin in the secretory granules and secreted in equimolar amounts, allowed studies of pancreatic beta cell function in vivo including in patients with diabetes. Subsequent studies have identified the specific proteases, prohormone convertases 1/3 and 2 and carboxypeptidase E, that are involved in the conversion of proinsulin to proinsulin intermediates and then to insulin. Disorders of (pro)insulin biosynthesis continue to illuminate important aspects of this pathway, revealing important connections to diabetes pathogenesis. Recent studies of patients with insulin gene mutations that cause permanent neonatal diabetes have identified key residues affecting the folding and structural organization of the preproinsulin molecule and its subsequent processing. These findings have renewed interest in the key role of endoplasmic reticulum function in insulin biosynthesis and the maintainance of normal beta cell health.

A model of action potentials and fast Ca2+ dynamics in pancreatic beta-cells.

We examined the ionic mechanisms mediating depolarization-induced spike activity in pancreatic beta-cells. We formulated a Hodgkin-Huxley-type ionic model for the action potential (AP) in these cells based on voltage- and current-clamp results together with measurements of Ca(2+) dynamics in wild-type and Kv2.1 null mouse islets. The model contains an L-type Ca(2+) current, a "rapid" delayed-rectifier K(+) current, a small slowly-activated K(+) current, a Ca(2+)-activated K(+) current, an ATP-sensitive K(+) current, a plasma membrane calcium-pump current and a Na(+) background current. This model, coupled with an equation describing intracellular Ca(2+) homeostasis, replicates beta-cell AP and Ca(2+) changes during one glucose-induced spontaneous spike, the effects of blocking K(+) currents with different inhibitors, and specific complex spike in mouse islets lacking Kv2.1 channels. The currents with voltage-independent gating variables can also be responsible for burst behavior. Original features of this model include new equations for L-type Ca(2+) current, assessment of the role of rapid delayed-rectifier K(+) current, and Ca(2+)-activated K(+) currents, demonstrating the important roles of the Ca(2+)-pump and background currents in the APs and bursts. This model provides acceptable fits to voltage-clamp, AP, and Ca(2+) concentration data based on in silico analysis.

Action potentials and insulin secretion: new insights into the role of Kv channels.

Coordinated electrical activity allows pancreatic beta-cells to respond to secretagogues with calcium entry followed by insulin secretion. Metabolism of glucose affects multiple membrane proteins including ion channels, transporters and pumps that collaborate in a cascade of electrical activity resulting in insulin release. Glucose induces beta-cell depolarization resulting in the firing of action potentials (APs), which are the primary electrical signal of the beta-cell. They are shaped by orchestrated activation of ion channels. Here we give an overview of the voltage-gated potassium (Kv) channels of the beta-cell, which are responsible in part for the falling phase of the AP, and how their regulation affects insulin secretion. beta cells contain several Kv channels allowing dynamic integration of multiple signals on repolarization of glucose-stimulated APs. Recent studies on Kv channel regulation by cAMP and arachidonic acid and on the Kv2.1 null mouse have greatly increased our understanding of beta-cell excitation-secretion coupling.

TRP channels of the pancreatic beta cell.

Orchestrated ion fluctuations within pancreatic islets regulate hormone secretion and maybe essential to processes such as apoptosis. A diverse set of ion channels allows for islet cells to respond to a variety of signals and dynamically regulate hormone secretion and glucose homeostasis (reviewed by Houamed et al. 2004). This chapter focuses on transient receptor potential (TRP)-related channels found within the beta cells of the islet and reviews their roles in both insulin secretion and apoptosis.

Improved outcomes in islet isolation and transplantation by the use of a novel hemoglobin-based O2 carrier.

During isolation, islets are exposed to warm ischemia. In this study, intraductal administration of oxygenated polymerized, stroma-free hemoglobin-pyridoxalated (Poly SFH-P) was performed to improve O2 delivery. Rat pancreata subjected to 30-min warm ischemia were perfused intraductally with collagenase in oxygenated Poly SFH-P/RPMI or RPMI (control). PO2 was increased by Poly SFH-P (381.7 +/- 35.3 mmHg vs. 202.3 +/- 28.2, p = 0.01) and pH maintained within physiological range (7.4-7.2 vs. 7.1-6.6, p = 0.009). Islet viability (77% +/- 4.6 vs. 63% +/- 4.7, p = 0.04) was improved and apoptosis lower with Poly SFH-P (caspase-3: 34,714 +/- 2167 vs. 45,985 +/- 1382, respectively, p = 0.01). Poly SFH-P improved islet responsiveness to glucose as determined by increased intracellular Ca2+ levels and improved insulin secretion (SI 5.4 +/- 0.1 vs. 3.1 +/- 0.2, p = 0.03). Mitochondrial integrity was improved in Poly SFH-P-treated islets, which showed higher percentage change in membrane potential after glucose stimulation (14.7% +/- 1.8 vs. 9.8 +/- 1.4, respectively, p < 0.05). O2 delivery by Poly SFH-P did not increase oxidative stress (GSH 7.1 +/- 2.9 nm/mg protein for Poly SFH-P vs. 6.8 +/- 2.4 control, p = 0.9) or oxidative injury (MDA 1.8 +/- 0.9 nmol/mg protein vs. 6.2 +/- 2.4, p = 0.19). Time to reach normoglycemia in transplanted diabetic nude mice was shorter (1.8 +/- 0.4 vs. 7 +/- 2.5 days, p = 0.02), and glucose tolerance improved in the Poly SFH-P group (AUC 8106 +/- 590 vs. 10,863 +/- 946, p = 0.03). Oxygenated Poly SFH-P improves islet isolation and transplantation outcomes by preserving mitochondrial integrity.

Reactive species and early manifestation of insulin resistance in type 2 diabetes.

The early stages of type 2 diabetes mellitus are characterized by the development of insulin resistance (IRe) in muscle cells and adipocytes with the concomitant loss of beta-cell compensation. We have extensively reviewed the literature related to metabolic and signalling pathways of reactive oxygen species (ROS) in regard to the coordinated development of oxidative stress and IRe. We considered the hypothesis that oxidative stress leads to IRe in muscle cells and adipocytes, but found that the data are more consistent with the hypothesis that the cellular mechanisms that protect against oxidative stress per se are capable of creating an ROS-dependent insulin-resistant state. Furthermore, ROS-induced mitochondrial dysfunction can lead to disruptions of lipid metabolism, increasing the intracellular lipid content, and, in addition, contribute to lipid-dependent IRe in myocytes. Together, these two ROS-activated pathways to IRe can contribute to a global state of profound resistance to insulin action. Therapeutic strategies should, therefore, be directed towards reducing insulin resistance without an increase in ROS production or concentration. Pharmacological or other approaches to IRe that result in the activation of mitochondrial biogenesis in particular could be highly beneficial in the prevention or treatment of both insulin resistance and type 2 diabetes.

Intragranular targeting of syncollin, but not a syncollinGFP chimera, inhibits regulated insulin exocytosis in pancreatic beta-cells.

Several proteins play a role in the mechanism of insulin exocytosis. However, these 'exocytotic proteins' have yet to account for the regulated aspect of insulin exocytosis, and other factors are involved. In pancreatic exocrine cells, the intralumenal zymogen granule protein, syncollin, is required for efficient regulated exocytosis, but it is not known whether intragranular peptides similarly influence regulated insulin exocytosis. Here, this issue has been addressed using expression of syncollin and a syncollin-green fluorescent protein (syncollinGFP) chimera in rat islet beta-cells as experimental tools. Syncollin is not normally expressed in beta-cells but adenoviral-mediated expression of both syncollin and syncollinGFP indicated that these were specifically targeted to the lumen of beta-granules. Syncollin expression in isolated rat islets had no effect on basal insulin secretion but significantly inhibited regulated insulin secretion stimulated by glucose (16.7 mM), glucagon-like peptide-1 (GLP-1) (10 nM) and glyburide (5 microM). Consistent with specific localization of syncollin to beta-granules, constitutive secretion was unchanged by syncollin expression in rat islets. Syncollin-mediated inhibition of insulin secretion was not due to inadequate insulin production. Moreover, secretagogue-induced increases in cytosolic intracellular Ca2+, which is a prerequisite for triggering insulin exocytosis, were unaffected in syncollin-expressing islets. Therefore, syncollin was most likely acting downstream of secondary signals at the level of insulin exocytosis. Thus, syncollin expression in beta-cells has highlighted the importance of intralumenal beta-granule peptide factors playing a role in the control of insulin exocytosis. In contrast to syncollin, syncollinGFP had no effect on insulin secretion, underlining its usefulness as a 'fluorescent tag' to track beta-granule transport and exocytosis in real time.

beta-Agonists and metabolism.

This review presents recent concepts of how beta-agonists affect glucose homeostasis by modulating insulin secretion, liver metabolism, and uptake of glucose into muscle, with attention to the influence of hypoglycemia on beta-agonist sensitivity and the effects of beta(3)-adrenergic receptor (beta(3)AR) polymorphisms on adipocyte metabolism. Specific beta(2)-agonist effects on the pancreatic beta cell result in increased insulin secretion, yet other mechanisms, such as increased glucagon secretion and hepatic effects, cause an overall increase in serum glucose and an apparent decrease in insulin sensitivity. Human studies confirm the presence of beta(2)ARs on pancreatic beta cells. Intensive treatment of diabetes mellitus with insulin, especially in type 1 diabetes, has led to increased incidence of hypoglycemia. Repeated episodes of hypoglycemia lead to unawareness of neuroglycopenia, a major limitation to intensive treatment. Hypoglycemic unawareness is associated with reduced beta-agonist sensitivity. Scrupulous avoidance of hypoglycemia over many weeks to months can restore beta-agonist sensitivity and improve detection of hypoglycemia. beta-agonists have also been employed to prevent hypoglycemia. beta-agonists can increase thermogenesis and lipolysis, leading to increased energy expenditure and decreased fat stores. While beta(1)ARs and beta(2)ARs mediate many of these actions, it is likely that beta(3)ARs in the adipocyte membrane also play an important role. Specific beta(3)AR subtypes have been associated with obesity and the metabolic syndrome.

Baculovirus-mediated gene transfer into pancreatic islet cells.

Baculovirus transduction is a gene transfer method that uses a moth cell virus for mammalian cells in culture, which results in a high-level prolonged expression. Here we demonstrate that recombinant baculoviruses can serve as efficient gene transfer vehicles for delivering foreign genes driven by mammalian promoters into human and mouse pancreatic islet cells. Existing methods, such as various transfection and electroporation techniques, either suffer from low efficiency or cause extensive membrane damage. Viral vectors have emerged as an important tool for gene delivery and expression in mammalian cells but suffer from several drawbacks, such as lengthy construction time and expression of viral genes. The baculovirus Autographa californica multiple nuclear polyhedrosis virus is widely used as a vector for expression of foreign genes in insect cells and, more recently, in some mammalian cells. Using several green fluorescent protein- and LacZ-expressing constructs in a cytomegalovirus promoter cassette, we obtained efficient gene expression in primary human and mouse islet cells. There was no impairment of glucose-stimulated intracellular free calcium responses after baculovirus infection. The safety and the relative ease of construction and propagation of the virus makes the baculovirus system a useful tool for facilitating the transfer of foreign genes.

Overexpression of Bcl-x(L) in beta-cells prevents cell death but impairs mitochondrial signal for insulin secretion.

To study effects of Bcl-x(L) in the pancreatic beta-cell, two transgenic lines were produced using different forms of the rat insulin promoter. Bcl-x(L) expression in beta-cells was increased 2- to 3-fold in founder (Fd) 1 and over 10-fold in Fd 2 compared with littermate controls. After exposure to thapsigargin (10 microM for 48 h), losses of cell viability in islets of Fd 1 and Fd 2 Bcl-x(L) transgenic mice were significantly lower than in islets of wild-type mice. Unexpectedly, severe glucose intolerance was observed in Fd 2 but not Fd 1 Bcl-x(L) mice. Pancreatic insulin content and islet morphology were not different from control in either transgenic line. However, Fd 2 Bcl-x(L) islets had impaired insulin secretory and intracellular free Ca(2+) ([Ca(2+)](i)) responses to glucose and KCl. Furthermore, insulin and [Ca(2+)](i) responses to pyruvate methyl ester (PME) were similarly reduced as glucose in Fd 2 Bcl-x(L) islets. Consistent with a mitochondrial defect, glucose oxidation, but not glycolysis, was significantly lower in Fd 2 Bcl-x(L) islets than in wild-type islets. Glucose-, PME-, and alpha-ketoisocaproate-induced hyperpolarization of mitochondrial membrane potential, NAD(P)H, and ATP production were also significantly reduced in Fd 2 Bcl-x(L) islets. Thus, although Bcl-x(L) promotes beta-cell survival, high levels of expression of Bcl-x(L) result in reduced glucose-induced insulin secretion and hyperglycemia due to a defect in mitochondrial nutrient metabolism and signaling for insulin secretion.

The status of voltage-dependent calcium channels in alpha 1E knock-out mice.

It has been hypothesized that R-type Ca currents result from the expression of the alpha(1E) gene. To test this hypothesis we examined the properties of voltage-dependent Ca channels in mice in which the alpha(1E) Ca channel subunit had been deleted. Application of omega-conotoxin GVIA, omega-agatoxin IVA, and nimodipine to cultured cerebellar granule neurons from wild-type mice inhibited components of the whole-cell Ba current, leaving a "residual" R current with an amplitude of approximately 30% of the total Ba current. A minor portion of this R current was inhibited by the alpha(1E)-selective toxin SNX-482, indicating that it resulted from the expression of alpha(1E). However, the majority of the R current was not inhibited by SNX-482. The SNX-482-sensitive portion of the granule cell R current was absent from alpha(1E) knock-out mice. We also identified a subpopulation of dorsal root ganglion (DRG) neurons from wild-type mice that expressed an SNX-482-sensitive component of the R current. However as with granule cells, most of the DRG R current was not blocked by SNX-482. We conclude that there exists a component of the R current that results from the expression of the alpha(1E) Ca channel subunit but that the majority of R currents must result from the expression of other Ca channel alpha subunits.

Beta-cell ion channels: keys to endodermal excitability.

Whereas pancreatic islet cells are not neurons, they are endodermally-derived specialized excitable cells that display many properties of neurons. Multiple ion channels in the pancreatic beta-cell regulate electrical excitability. Our focus for the last several years has been on the delayed rectifier (Kv) K+ channels, in an effort to define the individual roles of specific Kv channel genes in the overall regulation of insulin secretion. The many Kv channel genes, represented by more than 40 mammalian isoforms (termed Kv1 to Kv8), give rise to overlapping functions, primarily regulating repolarization of the plasma membrane. Experiments involving inhibition of Kv channel function have shown the important role Kv channels play in regulating beta-cell calcium oscillations in response to glucose stimulation. From our recent studies, we have concluded that although detectable mRNA for Kv1 family members is present in islets, Kv1 family channels are unlikely to play a significant role in the beta-cell, and we are now focusing on the roles of Kv2 and Kv3 channels.

Characterization of a Ca2+ release-activated nonselective cation current regulating membrane potential and [Ca2+]i oscillations in transgenically derived beta-cells.

Although stimulation of insulin secretion by glucose is regulated by coupled oscillations of membrane potential and intracellular Ca2+ ([Ca2+]i), the membrane events regulating these oscillations are incompletely understood. In the presence of glucose and tetraethylammonium, transgenically derived beta-cells (betaTC3-neo) exhibit coupled voltage and [Ca2+]i oscillations strikingly similar to those observed in normal islets in response to glucose. Using these cells as a model system, we investigated the membrane conductance underlying these oscillations. Alterations in delayed rectifier or Ca2+-activated K+ channels were excluded as a source of the conductance oscillations, as they are completely blocked by tetraethylammonium. ATP-sensitive K+ channels were also excluded, since the ATP-sensitive K+ channel blocker tolbutamide substituted for glucose in inducing [Ca2+]i oscillations. Thapsigargin, which depletes intracellular Ca2+ stores, and maitotoxin, an activator of nonselective cation channels, both converted the glucose-dependent [Ca2+]i oscillations into a sustained elevation. On the other hand, both SKF 96365, a blocker of Ca2+ store-operated channels, and external Na+ removal suppressed the glucose-stimulated [Ca2+]i oscillations. Maitotoxin activated a nonselective cation current in betaTC3 cells that was attenuated by removal of extracellular Na+ and by SKF 96365, in the same manner to a current activated in mouse beta-cells following depletion of intracellular Ca2+ stores. Currents similar to these are produced by the mammalian trp-related channels, a gene family that includes Ca2+ store-operated channels and inositol 1,4,5-trisphosphate-activated channels. We found several of the trp family genes were expressed in betaTC3 cells by reverse transcriptase polymerase chain reaction using specific primers, but by Northern blot analysis, mtrp-4 was the predominant message expressed. We conclude that a conductance underlying glucose-stimulated oscillations in beta-cells is provided by a Ca2+ store depletion-activated nonselective cation current, which is plausibly encoded by homologs of trp genes.