Kinetics Of Insulin Secretion Research Articles

Microphysiological pancreas-on-chip platform with integrated sensors to model endocrine function and metabolism.

Pancreatic in vitro research is of major importance to advance mechanistic understanding and development of treatment options for diseases such as diabetes mellitus. We present a thermoplastic-based microphysiological system aiming to model the complex microphysiological structure and function of the endocrine pancreas with concurrent real-time read-out capabilities. The specifically tailored platform enables self-guided trapping of single islets at defined locations: β-cells are assembled to pseudo-islets and injected into the tissue chamber using hydrostatic pressure-driven flow. The pseudo-islets can further be embedded in an ECM-like hydrogel mimicking the native microenvironment of pancreatic islets in vivo. Non-invasive real-time monitoring of the oxygen levels on-chip is realized by the integration of luminescence-based optical sensors to the platform. To monitor insulin secretion kinetics in response to glucose stimulation in a time-resolved manner, an automated cycling of different glucose conditions is implemented. The model's response to glucose stimulation can be monitored via offline analysis of insulin secretion and via specific changes in oxygen consumption due to higher metabolic activity of pseudo-islets at high glucose levels. To demonstrate applicability for drug testing, the effects of antidiabetic medications are assessed and changes in dynamic insulin secretion are observed in line with the respective mechanism of action. Finally, by integrating human pancreatic islet microtissues, we highlight the flexibility of the platform and demonstrate the preservation of long-term functionality of human endocrine pancreatic tissue.

Impaired pancreatic beta-cell function after a single dose of oral iron: A before-and-after (pre-post) study.

Although in vitro and animal studies have shown that iron loading in pancreatic beta cells impairs insulin secretion, no human studies have documented the acute effects of oral iron on beta-cell insulin secretory capacity. In the present study, we determined beta-cell insulin secretory capacity at baseline and after a single oral dose of iron (ferrous sulphate, 120 mg elemental iron) in healthy male individuals. Fifteen healthy male volunteers underwent an oral glucose tolerance test (OGTT) to document baseline glucose tolerance and insulin secretion kinetics (baseline OGTT). One week later, the same subjects underwent a second OGTT, 2 h after an oral dose of ferrous sulphate (120 mg of elemental iron) (post-iron OGTT). Changes in disposition index, insulin secretion kinetics, glucose tolerance, insulin resistance, insulin clearance and iron-related parameters in serum were determined. Compared to baseline OGTT, the areas under the curve (AUC) for serum iron and transferrin saturation increased by 125% and 118%, respectively, in the post-iron OGTT. The disposition index decreased by 20% (p = 0.009) and the AUC for glucose concentrations increased by 5.7% (p < 0.001) during the post-iron OGTT. The insulin secretion rate was marginally lower during the first hour (-3.5%, p = 0.63), but became significantly higher during the second hour (22%, p = 0.005) of the post-iron OGTT. Insulin resistance and insulin clearance rate were not affected by iron intake. The decrease in disposition index and glucose tolerance observed after the oral dose of iron points to an acute iron-induced impairment in pancreatic beta-cell insulin secretory capacity.

Beta‐cell Prohormone Convertase 1/3 Plays a Larger Role in Glucose Homeostasis Than Beta‐cell Prohormone Convertase 2 in Mice

Insulin is synthesized in pancreatic beta cells from its precursor proinsulin, which is cleaved by the prohormone convertases 1/3 (PCSK1) and 2 (PCSK2) to generate mature insulin. In patients with type 1 or type 2 diabetes, proinsulin processing to mature insulin is impaired and elevated circulating proinsulin:insulin ratios are found in both conditions. It is unknown whether the beta‐cell prohormone processing impairments observed in diabetes contribute to or are secondary consequences of beta‐cell failure. Given the key role of PCSK1 and PCSK2 in insulin synthesis and beta‐cell function, we hypothesized that beta‐cell PCSK1 or PCSK2 deficiency would result in beta‐cell dysfunction and glucose intolerance.Beta‐cell specific knockout mouse models of Pcsk1 (Pcsk1betaKO) and Pcsk2 (Pcsk2betaKO) were generated using cre‐lox recombination and monitored for changes in glycemia on chow and high‐fat (HF) diets. Neither Pcsk1betaKO or Pcsk2betaKO chow‐fed animals displayed hyperglycemia or impaired glucose tolerance in the first 14 weeks of life. By 26 weeks of age Pcsk1betaKO, but not Pcsk2betaKO, chow‐fed male mice displayed fasting hyperglycemia and impaired glucose tolerance. After 19 weeks of HF diet, 3 of 5 Pcsk1betaKO male mice developed diabetes (fasting glycemia &gt; 16mM), while no hyperglycemia was observed in Pcsk2betaKO mice up to 30 weeks of diet duration. Pcsk1betaKO mice displayed elevated islet and plasma (pro)insulin levels, decreased islet mature insulin levels, translucent insulin granules, and trended toward increased beta‐cell area in the pancreas. Despite altered insulin biosynthesis and immature granules, Pcsk1betaKO islets displayed similar insulin secretion kinetics to Pcsk1 wild‐type islets ex vivo.Our data suggest that Pcsk1 plays a larger role in proinsulin processing and beta‐cell function in mice than Pcsk2. However, despite severe impairments in insulin biosynthesis, Pcsk1‐deficient beta cells compensate remarkably well at early ages and hyperglycemia is only observed in states of increased beta‐cell secretory demand (mild insulin resistance associated with aging or HF diet in mice). Thus, impaired Pcsk1‐mediated prohormone processing, but not Pcsk2‐mediated processing, in beta cells increases diabetes susceptibility in mice.Support or Funding InformationFunding was provided by the Canadian Institutes of Health Research and Canucks for Kids Fund Childhood Diabetes Laboratories

Non-invasive marker-independent high content analysis of a microphysiological human pancreas-on-a-chip model

The increasing prevalence of diabetes, its heterogeneity, and the limited number of treatment options drive the need for physiologically relevant assay platforms with human genetic background that have the potential to improve mechanistic understanding and e\\xpedite diabetes-related research and treatment. In this study, we developed an endocrine pancreas-on-a-chip model based on a tailored microfluidic platform, which enables self-guided trapping of single human pseudo-islets. Continuous, low-shear perfusion provides a physiologically relevant microenvironment especially important for modeling and monitoring of the endocrine function as well as sufficient supply with nutrients and oxygen. Human pseudo-islets, generated from the conditionally immortalized EndoC-βH3 cell line, were successfully injected by hydrostatic pressure-driven flow without altered viability. To track insulin secretion kinetics in response to glucose stimulation in a time-resolved manner, dynamic sampling of the supernatant as well as non-invasive real-time monitoring using Raman microspectroscopy was established on-chip. Dynamic sampling indicated a biphasic glucose-stimulated insulin response. Raman microspectroscopy allowed to trace glucose responsiveness in situ and to visualize different molecular structures such as lipids, mitochondria and nuclei. In-depth spectral analyses demonstrated a glucose stimulation-dependent, increased mitochondrial activity, and a switch in lipid composition of insulin secreting vesicles, supporting the high performance of our pancreas-on-a-chip model.

Calcium signaling and secretory granule pool dynamics underlie biphasic insulin secretion and its amplification by glucose: experiments and modeling.

Glucose-stimulated insulin secretion from pancreatic β-cells is controlled by a triggering pathway that culminates in calcium influx and regulated exocytosis of secretory granules, and by a less understood amplifying pathway that augments calcium-induced exocytosis. In response to an abrupt increase in glucose concentration, insulin secretion exhibits a first peak followed by a lower sustained second phase. This biphasic secretion pattern is disturbed in diabetes. It has been attributed to depletion and subsequent refilling of a readily releasable pool of granules or to the phasic cytosolic calcium dynamics induced by glucose. Here, we apply mathematical modeling to experimental data from mouse islets to investigate how calcium and granule pool dynamics interact to control dynamic insulin secretion. Experimental calcium traces are used as inputs in three increasingly complex models of pool dynamics, which are fitted to insulin secretory patterns obtained using a set of protocols of glucose and tolbutamide stimulation. New calcium and secretion data for so-called staircase protocols, in which the glucose concentration is progressively increased, are presented. These data can be reproduced without assuming any heterogeneity in the model, in contrast to previous modeling, because of nontrivial calcium dynamics. We find that amplification by glucose can be explained by increased mobilization and priming of granules. Overall, our results indicate that calcium dynamics contribute substantially to shaping insulin secretion kinetics, which implies that better insight into the events creating phasic calcium changes in human β-cells is needed to understand the cellular mechanisms that disturb biphasic insulin secretion in diabetes.

Nutritional recovery from a low-protein diet during pregnancy does not restore the kinetics of insulin secretion and Ca2+ or alterations in the cAMP/PKA and PLC/PKC pathways in islets from adult rats.

We investigated the insulin release induced by glucose, the Ca2+ oscillatory pattern, and the cyclic AMP (cAMP)/protein kinase A (PKA) and phospholipase C (PLC)/protein kinase C (PKC) pathways in islets from adult rats that were reared under diets with 17% protein (C) or 6% protein (LP) during gestation, suckling, and after weaning and in rats receiving diets with 6% protein during gestation and 17% protein after birth (R). First-phase glucose-induced insulin secretion was reduced in LP and R islets, and the second phase was partially restored in the R group. Glucose stimulation did not modify intracellular Ca2+ concentration, but it reduced the Ca2+ oscillatory frequency in the R group compared with the C group. Intracellular cAMP concentration was higher and PKA-Cα expression was lower in the R and LP groups compared with the C group. The PKCα content in islets from R rats was lower than that in C and LP rats. Thus, nutritional recovery from a low-protein diet during fetal life did not repair the kinetics of insulin release, impaired Ca2+ handling, and altered the cAMP/PKA and PLC/PKC pathways.

Insulin secretion kinetics from single islets reveals distinct subpopulations

Type II diabetes progresses with inadequate insulin secretion and prolonged elevated circulating glucose levels. Also, pancreatic islets isolated for transplantation or tissue engineering can be exposed to glucose over extended timeframe. We hypothesized that isolated pancreatic islets can secrete insulin over a prolonged period of time when incubated in glucose solution and that not all islets release insulin in unison. Insulin secretion kinetics was examined and modeled from single mouse islets in response to chronic glucose exposure (2.8-20 mM). Results with single islets were compared to those from pools of islets. Kinetic analysis of 58 single islets over 72 h in response to elevated glucose revealed distinct insulin secretion profiles: slow-, fast-, and constant-rate secretors, with slow-secretors being most prominent (ca., 50%). Variations in the temporal response to glucose therefore exist. During short-term (<4 h) exposure to elevated glucose few islets are responding with sustained insulin release. The model allowed studying the influence of islet size, revealing no clear effect. At high-glucose concentrations, when secretion is normalized to islet volume, the tendency is that smaller islets secrete more insulin. At high-glucose concentrations, insulin secretion from single islets is representative of islet populations, while under low-glucose conditions pooled islets did not behave as single ones. The characterization of insulin secretion over prolonged periods complements studies on insulin secretion performed over short timeframe. Further investigation of these differences in secretion profiles may resolve open-ended questions on pre-diabetic conditions and transplanted islets performance. This study deliberates the importance of size of islets in insulin secretion. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:1059-1068, 2018.

The Second Phase of Insulin Secretion in Nondiabetic Islet-Grafted Recipients Is Altered and Can Predict Graft Outcome.

Islet transplantation (IT) can treat patients with severely unstable type 1 diabetes. Prehepatic kinetics of insulin secretion (ISec) in two phases can be calculated by C-peptide levels during meal tests. We proposed to describe the ISec profile after a mixed-meal tolerance test (MMTT) in IT recipients and to determine whether the calculated ISec indexes can predict graft outcome. We analyzed 34 MMTT among 11 patients who underwent IT between 2011 and 2016 and compared them with healthy controls and patients with type 2 diabetes (T2D). ISec indexes and insulin sensitivity were calculated from models of Van Cauter, Breda, and Mari after MMTT. Graft success was defined by total insulin independence without any criteria for diabetes. In patients with successful IT, the first- and second-phase ISec indexes were lower than those of controls (P < 0.001) and did not differ from those of the T2D group. Nevertheless, insulin sensitivity of IT recipients was similar to that of the control group and higher than that of the T2D group. The index of the second phase of ISec ɸS was correlated with total infused islet equivalents (IEQs), was a good predictor of diabetes (re)occurrence, and allowed us to calculate 9500 IEQ/kg as the minimum needed to reach insulin independence. We showed that indexes from the first and second phases of ISec are altered in insulin-independent IT recipients. Higher sensitivity distinguishes them from patients with T2D. Even in insulin-independent patients, IT remains a marginal mass model. Moreover, ɸS can estimate transplanted islet mass and predict IT recipient outcomes.

Islet Encapsulation: Physiological Possibilities and Limitations.

A logical cure for type 1 diabetes (T1D) involves replacing the lost insulin-producing cells with new ones, preferably cells from a well-characterized and unlimited source of human insulin-producing cells. This straightforward and simple solution to provide a cure for T1D is immensely attractive but entails at least two inherent and thus far unresolved hurdles: 1) provision of an unlimited source of functional human insulin-producing cells and 2) prevention of rejection without the side effects of systemic immunosuppression. Generation of transplantable insulin-producing cells from human embryonic stem cells or induced pluripotent stem cells is at present close to reality, and we are currently awaiting the first clinical studies. Focus is now directed to foster development of novel means to control the immune system to enable large-scale clinical application. Encapsulation introduces a physical barrier that prevents access of immune cells to the transplanted cells but also hinders blood vessel ingrowth. Therefore, oxygen, nutrient, and hormonal passage over the encapsulation membrane is solely dependent on diffusion over the immune barrier, contributing to delays in glucose sensing and insulin secretion kinetics. This Perspective focuses on the physiological possibilities and limitations of an encapsulation strategy to establish near-normoglycemia in subjects with T1D, assuming that glucose-responsive insulin-producing cells are available for transplantation.

Ca2+ channel clustering with insulin-containing granules is disturbed in type 2 diabetes.

Loss of first-phase insulin secretion is an early sign of developing type 2 diabetes (T2D). Ca2+ entry through voltage-gated L-type Ca2+ channels triggers exocytosis of insulin-containing granules in pancreatic β cells and is required for the postprandial spike in insulin secretion. Using high-resolution microscopy, we have identified a subset of docked insulin granules in human β cells and rat-derived clonal insulin 1 (INS1) cells for which localized Ca2+ influx triggers exocytosis with high probability and minimal latency. This immediately releasable pool (IRP) of granules, identified both structurally and functionally, was absent in β cells from human T2D donors and in INS1 cells cultured in fatty acids that mimic the diabetic state. Upon arrival at the plasma membrane, IRP granules slowly associated with 15 to 20 L-type channels. We determined that recruitment depended on a direct interaction with the synaptic protein Munc13, because expression of the II–III loop of the channel, the C2 domain of Munc13-1, or of Munc13-1 with a mutated C2 domain all disrupted L-type channel clustering at granules and ablated fast exocytosis. Thus, rapid insulin secretion requires Munc13-mediated recruitment of L-type Ca2+ channels in close proximity to insulin granules. Loss of this organization underlies disturbed insulin secretion kinetics in T2D.

The effect of islet culture on the biphasic pattern of fuel-induced insulin secretion

The insulin secretion pattern by mouse islets is reported to differ from that of human and rat islets in that a strong first phase is followed by an elevated plateau instead of a slowly ascending second phase. This has led to the argument that mouse islets or beta cells may not be a good experimental model. Here, we have tested the role of islet culture on shaping the kinetics of insulin secretion.

MiR-124a expression contributes to the monophasic pattern of insulin secretion in islets from pregnant rats submitted to a low-protein diet

To evaluate the role of miR-124a in the regulation of genes involved in insulin exocytosis and its effects on the kinetics of insulin secretion in pancreatic islets from pregnant rats submitted to a low-protein diet. Adult control non-pregnant (CNP) and control pregnant (CP) rats were fed a normal protein diet (17%), whereas low-protein non-pregnant (LPNP) and low-protein pregnant (LPP) rats were fed a low-protein diet (6%) from days 1 to 15 of pregnancy. Kinetics of the glucose-induced insulin release and measurement of [Ca2+]i in pancreatic islets were assessed by standard protocols. The miR-124a expression and gene transcriptions from pancreatic islets were determined by real-time polymerase chain reaction. In islets from LPP rats, the first phase of insulin release was abrogated. The AUC [Ca2+]i from the LPP group was lower compared with the other groups. miR-124a expression was reduced by a low-protein diet. SNAP-25 mRNA, protein expression, and Rab3A protein content were lower in the LPP rats than in CP rats. Syntaxin 1A and Kir6.2 mRNA levels were decreased in islets from low-protein rats compared with control rats, whereas their protein content was reduced in islets from pregnant rats. Loss of biphasic insulin secretion in islets from LPP rats appears to have resulted from reduced [Ca2+]i due, at least in part, to Kir6.2 underexpression and from the changes in exocytotic elements that are influenced either directly or indirectly by miR-124a.

A pumpless microfluidic device driven by surface tension for pancreatic islet analysis.

We present a novel pumpless microfluidic array driven by surface tension for studying the physiology of pancreatic islets of Langerhans. Efficient fluid flow in the array is achieved by surface tension-generated pressure as a result of inlet and outlet size differences. Flow properties are characterized in numerical simulation and further confirmed by experimental measurements. Using this device, we perform a set of biological assays, which include real-time fluorescent imaging and insulin secretion kinetics for both mouse and human islets. Our results demonstrate that this system not only drastically simplifies previously published experimental protocols for islet study by eliminating the need for external pumps/tubing and reducing the volume of solution consumption, but it also achieves a higher analytical spatiotemporal resolution due to efficient flow exchanges and the extremely small volume of solutions required. Overall, the microfluidic platform presented can be used as a potential powerful tool for understanding islet physiology, antidiabetic drug development, and islet transplantation.

Secretagogin affects insulin secretion in pancreatic β-cells by regulating actin dynamics and focal adhesion.

Secretagogin (SCGN), a Ca2+-binding protein having six EF-hands, is selectively expressed in pancreatic β-cells and neuroendocrine cells. Previous studies suggested that SCGN enhances insulin secretion by functioning as a Ca2+-sensor protein, but the underlying mechanism has not been elucidated. The present study explored the mechanism by which SCGN enhances glucose-induced insulin secretion in NIT-1 insulinoma cells. To determine whether SCGN influences the first or second phase of insulin secretion, we examined how SCGN affects the kinetics of insulin secretion in NIT-1 cells. We found that silencing SCGN suppressed the second phase of insulin secretion induced by glucose and H2O2, but not the first phase induced by KCl stimulation. Recruitment of insulin granules in the second phase of insulin secretion was significantly impaired by knocking down SCGN in NIT-1 cells. In addition, we found that SCGN interacts with the actin cytoskeleton in the plasma membrane and regulates actin remodelling in a glucose-dependent manner. Since actin dynamics are known to regulate focal adhesion, a critical step in the second phase of insulin secretion, we examined the effect of silencing SCGN on focal adhesion molecules, including FAK (focal adhesion kinase) and paxillin, and the cell survival molecules ERK1/2 (extracellular-signal-regulated kinase 1/2) and Akt. We found that glucose- and H2O2-induced activation of FAK, paxillin, ERK1/2 and Akt was significantly blocked by silencing SCGN. We conclude that SCGN controls glucose-stimulated insulin secretion and thus may be useful in the therapy of Type 2 diabetes.

Donald F. Steiner: great scientist, close friend, real 'Mensch'.

Donald F. Steiner: great scientist, close friend, real 'Mensch'.

Serum α-hydroxybutyrate (α-HB) predicts elevated 1 h glucose levels and early-phase β-cell dysfunction during OGTT

ObjectiveSerum α-hydroxybutyrate (α-HB) is elevated in insulin resistance and diabetes. We tested the hypothesis that the α-HB level predicts abnormal 1 h glucose levels and β-cell dysfunction inferred from plasma...

Predictive values of serum insulin kinetics for reversion of impaired glucose tolerance to normal glucose tolerance and the effects of voglibose treatment: a retrospective post hoc analysis of a Japanese phase III study

In a phase III study, voglibose was shown to reduce the risk of development of type 2 diabetes mellitus (T2DM) by 40.5 % in Japanese individuals with impaired glucose tolerance (IGT), and appeared to promote reversion of IGT to normal glucose tolerance (NGT). In a retrospective, post hoc analysis, data from this study, plus follow-up findings from subjects who achieved NGT during the study and who were off-treatment, were analyzed to investigate serum insulin kinetic parameters which might be predictors of IGT reversion to NGT, and maintenance of NGT once achieved. The effects of voglibose on serum insulin kinetics in individuals with IGT were also assessed. Subjects with IGT (n = 1778) were randomized to receive voglibose (0.6 mg/day) or placebo for a mean of 48.1 weeks. During treatment, 1053 subjects achieved NGT, 569 continued to have IGT, and 156 developed T2DM. Analysis of baseline characteristics in each outcome group showed that subjects with higher 30-min serum immunoreactive insulin (IRI) levels in a 75 g oral glucose tolerance test (OGTT) or higher insulinogenic indexes at baseline were more likely to achieve NGT, whether they received voglibose or placebo. Among subjects who achieved NGT, the mean increase in OGTT 30-min IRI level from baseline to endpoint was significantly greater after treatment with voglibose than with placebo. Individuals who had higher OGTT 30-min IRI levels when achieving NGT seemed more likely to sustain this state. Thus, insulin secretion kinetics appeared to predict reversion of IGT to NGT and maintenance of NGT once achieved.

Systematic prevention of bubble formation and accumulation for long-term culture of pancreatic islet cells in microfluidic device.

Reliable long-term cell culture in microfluidic system is limited by air bubble formation and accumulation. In this study, we developed a bubble removal system capable of both trapping and discharging air bubbles in a consistent and reliable manner. Combined with PDMS (Polydimethylsiloxane) hydrophilic surface treatment and vacuum filling, a microfluidic perifusion system equipped with the bubble trap was successfully applied for long-term culture of mouse pancreatic islets with no bubble formation and no flow interruption. In addition to demonstrating normal cell viability and islet morphology, post-cultured islets exhibited normal insulin secretion kinetics, intracellular calcium signaling, and changes in mitochondrial potentials in response to glucose challenge. This design could be easily adapted by other microfluidic systems due to its simple design, ease of fabrication, and portability.

Combinatorial insulin secretion dynamics of recombinant hepatic and enteroendocrine cells

One of the most promising cell-based therapies for combating insulin-dependent diabetes entails the use of genetically engineered non-β cells that secrete insulin in response to physiologic stimuli. A normal pancreatic β cell secretes insulin in a biphasic manner in response to glucose. The first phase is characterized by a transient stimulation of insulin to rapidly lower the blood glucose levels, which is followed by a second phase of insulin secretion to sustain the lowered blood glucose levels over a longer period of time. Previous studies have demonstrated hepatic and enteroendocrine cells to be appropriate hosts for recombinant insulin expression. Due to different insulin secretion kinetics from these cells, we hypothesized that a combination of the two cell types would mimic the biphasic insulin secretion of normal β cells with higher fidelity than either cell type alone. In this study, insulin secretion experiments were conducted with two hepatic cell lines (HepG2 and H4IIE) transduced with 1 of 3 adenoviruses expressing the insulin transgene and with a stably transfected recombinant intestinal cell line (GLUTag-INS). Insulin secretion was stimulated by exposing the cells to glucose only (hepatic cells), meat hydrolysate only (GLUTag-INS), or to a cocktail of the two secretagogues. It was found experimentally that the recombinant hepatic cells secreted insulin in a more sustained manner, whereas the recombinant intestinal cell line exhibited rapid insulin secretion kinetics upon stimulation. The insulin secretion profiles were computationally combined at different cell ratios to arrive at the combinatorial kinetics. Results indicate that combinations of these two cell types allow for tuning the first and second phase of insulin secretion better than either cell type alone. This work provides the basic framework in understanding the secretion kinetics of the combined system and advances it towards preclinical studies.

In vitro insulin secretion by pancreatic tissue from infants with diazoxide-resistant congenital hyperinsulinism deviates from model predictions

Congenital hyperinsulinism (CHI) is the major cause of persistent neonatal hypoglycemia. CHI most often occurs due to mutations in the ABCC8 (which encodes sulfonylurea receptor 1) or KCNJ11 (which encodes the potassium channel Kir6.2) gene, which result in a lack of functional KATP channels in pancreatic β cells. Diffuse forms of CHI (DiCHI), in which all β cells are abnormal, often require subtotal pancreatectomy, whereas focal forms (FoCHI), which are characterized by localized hyperplasia of abnormal β cells, can be cured by resection of the lesion. Here, we characterized the in vitro kinetics of insulin secretion by pancreatic fragments from 6 DiCHI patients and by focal lesion and normal adjacent pancreas from 18 FoCHI patients. Responses of normal pancreas were similar to those reported for islets from adult organ donors. Compared with normal pancreas, basal insulin secretion was elevated in both FoCHI and DiCHI tissue. Affected tissues were heterogeneous in their secretory responses, with increased glucose levels often producing a rapid increase in insulin secretion that could be followed by a paradoxical decrease below prestimulatory levels. The KATP channel blocker tolbutamide was consistently ineffective in stimulating insulin secretion; conversely, the KATP channel activator diazoxide often caused an unanticipated increase in insulin secretion. These observed alterations in secretory behavior were similar in focal lesion and DiCHI tissue, and independent of the specific mutation in ABCC8 or KCNJ11. They cannot be explained by classic models of β cell function. Our results provide insight into the excessive and sometimes paradoxical changes in insulin secretion observed in CHI patients with inactivating mutations of KATP channels.