Reactive oxygen species stimulate insulin secretion in rat pancreatic islets: studies using mono-oleoyl-glycerol

Chronic exposure (24–72 hrs) of pancreatic islets to elevated glucose and fatty acid leads to glucolipoxicity characterized by basal insulin hypersecretion and impaired glucose-stimulated insulin secretion (GSIS). Our aim was to determine the mechanism for basal hypersecretion of insulin. We used mono-oleoyl-glycerol (MOG) as a tool to rapidly increase lipids in isolated rat pancreatic ß-cells and in the clonal pancreatic ß-cell line INS-1 832/13. MOG (25–400 µM) stimulated basal insulin secretion from ß-cells in a concentration dependent manner without increasing intracellular Ca²⁺ or O₂ consumption. Like GSIS, MOG increased NAD(P)H and reactive oxygen species (ROS). The mitochondrial reductant ß-hydroxybutyrate (ß-OHB) also increased the redox state and ROS production, while ROS scavengers abrogated secretion. Diazoxide (0.4 mM) did not prevent the stimulatory effect of MOG, confirming that the effect was independent of the K_ATP-dependent pathway of secretion. MOG was metabolized to glycerol and long-chain acyl-CoA (LC-CoA), whereas, acute oleate did not similarly increase LC-CoA. Inhibition of diacylglycerol kinase (DGK) did not mimic the effect of MOG on insulin secretion, indicating that MOG did not act primarily by inhibiting DGK. Inhibition of acyl-CoA synthetase (ACS) reduced the stimulatory effect of MOG on basal insulin secretion by 30% indicating a role for LC-CoA. These data suggest that basal insulin secretion is stimulated by increased ROS production, due to an increase in the mitochondrial redox state independent of the established components of GSIS.     

Regulation of K(ATP) channel by 17β-estradiol in pancreatic β-cells

ATP-sensitive potassium channels (K_ATP) regulate electrical activity and insulin secretion in pancreatic β-cells. When glucose concentration increases, the [ATP]/[ADP] ratio rises closing K_ATP channels, and the membrane potential depolarizes, triggering insulin secretion. This pivotal role of K_ATP channels is used not only by glucose but also by neurotransmitters, hormones and other physiological agents to modulate electrical and secretory β-cell response.In recent years, it has been demonstrated that estrogens and estrogen receptors are involved in glucose homeostasis, and that they can modulate the electrical activity and insulin secretion of pancreatic β-cells. The hormone 17β-estradiol (E2), at physiological levels, is implicated in maintaining normal insulin sensitivity for β-cell function. Long term exposure to E2 increases insulin content, insulin gene expression and insulin release via the estrogen receptor α (ERα), while rapid responses to E2 can regulate K_ATP channels increasing cGMP levels through the estrogen receptor β (ERβ) and type A guanylate cyclase receptor (GC-A). This review summarizes the main actions of 17β-estradiol on K_ATP channels and the subsequent insulin release in pancreatic β-cells.     

Current status of the E23K Kir6.2 polymorphism: implications for type-2 diabetes

The ATP-sensitive potassium (K_ATP) channel couples membrane excitability to cellular metabolism and is a critical mediator in the process of glucose-stimulated insulin secretion. Increasing numbers of K_ATP channel polymorphisms are being described and linked to altered insulin secretion indicating that genes encoding this ion channel could be susceptibility markers for type-2 diabetes. Genetic variation of K_ATP channels may result in altered -cell electrical activity, glucose homeostasis, and increased susceptibility to type-2 diabetes. Of particular interest is the Kir6.2 E23K polymorphism, which is linked to increased susceptibility to type-2 diabetes in Caucasian populations and may also be associated with weight gain and obesity, both of which are major diabetes risk factors. This association highlights the potential contribution of both genetic and environmental factors to the development and progression of type-2 diabetes. In addition, the common occurrence of the E23K polymorphism in Caucasian populations may have conferred an evolutionary advantage to our ancestors. This review will summarize the current status of the association of K_ATP channel polymorphisms with type-2 diabetes, focusing on the possible mechanisms by which these polymorphisms alter glucose homeostasis and offering insights into possible evolutionary pressures that may have contributed to the high prevalence of K_ATP channel polymorphisms in the Caucasian population.This work was supported by funding from the Canadian Diabetes Association (CDA) in honor of Gordon M. Stevenson, the Alberta Heritage Foundation for Medical Research (AHFMR), and the Canadian Institutes of Health Research (CIHR). M.J.R. is supported by AHFMR and CDA Scholarships. P.E.L. received salary support as an AHFMR Scholar and CIHR New Investigator     

Chronic palmitic acid-induced lipotoxicity correlates with defective trafficking of ATP sensitive potassium channels in pancreatic β cells

Lipotoxicity is associated with a high level of fatty acid accumulation in pancreatic β-cells. An overload of free fatty acids contributes to pancreatic β-cell apoptosis and dysfunction. Insulin secretion involves sequential ionic events upon glucose stimulation. ATP sensitive potassium (K_ATP) channels serve as glucose sensors and effectively initiate glucose-stimulated insulin secretion. This study investigated the effects of lipotoxicity on the trafficking of K_ATP channels in pancreatic β cells using chronic palmitic acid –injected mice and treated insulinoma cells. The chronic palmitic acid -injected mice displayed type II diabetic characteristics. The pancreatic sections of these mice exhibited a decrease in the expression of K_ATP channels. We then tested the time and dose effects of palmitic acid on the cell viability of INS-1 cells. We observed a significant decrease in the surface expression of K_ATP channels after 72 h of treatment with 0.4 mM palmitic acid. In addition, this treatment induced pancreatic β-cell apoptosis by increasing cleaved caspase 3 protein level. Our results demonstrated cotreatment with glibenclamide, the sulfonylurea compounds for type II diabetes mellitus, in palmitic acid -treated cells reduces cell death and recovers the glucose stimulated insulin secretion through increasing the surface expression of K_ATP channels. Importantly, glibenclamide also improved glucose tolerance, triglyceride concentration, and insulin sensitivity in the palmitic acid-injected mice. In conclusion, an increase in the surface expression of K_ATP channels restores insulin secretion, reduces pancreatic β-cell’s apoptosis, highlighting correct trafficking of K_ATP channels is important in survival of β-cells during lipotoxicity.     

Caveolin-1 is essential for glimepiride-induced insulin secretion in the pancreatic betaTC-6 cell line

The K_ATP channels play a pivotal role in the complex mechanism of insulin secretion. K_ATP channels represent the target of sulphonylureas, a class of drugs widely used in type 2 diabetes to stimulate insulin secretion. We previously showed that caveolin-1 depletion impairs action of the sulphonylurea glimepiride in human endothelial cells. The aim of this work was to investigate the possible role of caveolin-1 in glimepiride-induced insulin secretion. Caveolin-1 was depleted using siRNA method in the pancreatic βTC-6 cell line. Then stimulation of insulin secretion was performed with different secretagogues (glucose, KCl, and glimepiride). Here, we show that βTC-6 caveolin-1 depleted cells maintained high rate of insulin secretion after KCl, but not after glucose and glimepiride stimulation. Moreover, we find a direct interaction between caveolin-1 and Kir6.2, one of the K_ATP channel subunit. These results demonstrate that Cav-1 plays a critical role for glucose and sulfonylurea-stimulated insulin secretion.     

ARA290 Improves Insulin Release and Glucose Tolerance in Type 2 Diabetic Goto-Kakizaki Rats

Effects of ARA290 on glucose homeostasis were studied in type 2 diabetic Goto-Kakizaki (GK) rats. In GK rats receiving ARA290 daily for up to 4 wks, plasma glucose concentrations were lower after 3 and 4 wks, and hemoglobin A_1c (Hb A_1c) was reduced by ~20% without changes in whole body and hepatic insulin sensitivity. Glucose-stimulated insulin secretion was increased in islets from ARA290-treated rats. Additionally, in response to glucose, carbachol and KCl, islet cytoplasmic free Ca²⁺ concentrations, [Ca²⁺]_i, were higher and the frequency of [Ca²⁺]_i oscillations enhanced compared with placebo. ARA290 also improved stimulus–secretion coupling for glucose in GK rat islets, as shown by an improved glucose oxidation rate, ATP production and acutely enhanced glucose-stimulated insulin secretion. ARA290 also exerted an effect distal to the ATP-sensitive potassium (K_ATP) channel on the insulin exocytotic pathway, since the insulin response was improved following islet depolarization by KCl when K_ATP channels were kept open by diazoxide. Finally, inhibition of protein kinase A completely abolished effects of ARA290 on insulin secretion. In conclusion, ARA290 improved glucose tolerance without affecting hematocrit in diabetic GK rats. This effect appears to be due to improved β-cell glucose metabolism and [Ca²⁺]_i handling, and thereby enhanced glucose-induced insulin release.     

K<Subscript>ATP</Subscript> channel polymorphism is associated with left ventricular size in hypertensive individuals: a large-scale community-based study

ATP-sensitive K⁺ (K_ATP) channel mutations have been identified in individuals with dilated cardiomyopathy and overt heart failure. Here, a common E23K functional polymorphism in the Kir6.2 channel pore versus cardiac phenotype was studied in a cross-sectional community-based cohort (n = 2,031). The KK genotype was associated with greater left ventricular size among subjects with increased stress load due to hypertension. These findings implicate Kir6.2 K23 as a risk factor for adverse subclinical myocardial remodeling, and underscore the significance of cardiac K_ATP channels within the population.     

Long chain CoA esters as competitive antagonists of phosphatidylinositol 4,5-bisphosphate activation in Kir channels

Long chain fatty acid esters of coenzyme A (LC-CoA) are potent activators of ATP-sensitive (K(ATP)) channels, and elevated levels have been implicated in the pathophysiology of type 2 diabetes. This stimulatory effect is thought to involve a mechanism similar to phosphatidylinositol 4,5-bisphosphate (PIP2), which activates all known inwardly rectifying potassium (Kir) channels. However, the effect of LC-CoA on other Kir channels has not been well characterized. In this study, we show that in contrast to their stimulatory effect on K(ATP) channels, LC-CoA (e.g. oleoyl-CoA) potently and reversibly inhibits all other Kir channels tested (Kir1.1, Kir2.1, Kir3.4, Kir7.1). We also demonstrate that the inhibitory potency of the LC-CoA increases with the chain length of the fatty acid chain, while both its activatory and inhibitory effects critically depend on the presence of the 3'-ribose phosphate on the CoA group. Biochemical studies also demonstrate that PIP2 and LC-CoA bind with similar affinity to the C-terminal domains of Kir2.1 and Kir6.2 and that PIP2 binding can be competitively antagonized by LC-CoA, suggesting that the mechanism of LC-CoA inhibition involves displacement of PIP2. Furthermore, we demonstrate that in contrast to its stimulatory effect on K(ATP) channels, phosphatidylinositol 3,4-bisphosphate has an inhibitory effect on Kir1.1 and Kir2.1. These results demonstrate a bi-directional modulation of Kir channel activity by LC-CoA and phosphoinositides and suggest that changes in fatty acid metabolism (e.g. LC-CoA production) could have profound and widespread effects on cellular electrical activity.     

Activation of activin type IB receptor signals in pancreatic β cells leads to defective insulin secretion through the attenuation of ATP-sensitive K channel activity

In studies of gene-ablated mice, activin signaling through activin type IIB receptors (ActRIIB) and Smad2 has been shown to regulate not only pancreatic β cell mass but also insulin secretion. However, it still remains unclear whether gain of function of activin signaling is involved in the modulation of pancreatic β cell mass and insulin secretion. To identify distinct roles of activin signaling in pancreatic β cells, the Cre-loxP system was used to activate signaling through activin type IB receptor (ActRIB) in pancreatic β cells. The resultant mice (pancreatic β cell-specific ActRIB transgenic (Tg) mice; ActRIBCAβTg) exhibited a defect in glucose-stimulated insulin secretion (GSIS) and a progressive impairment of glucose tolerance. Patch-clamp techniques revealed that the activity of ATP-sensitive K⁺ channels (K_ATP channels) was decreased in mutant β cells. These results indicate that an appropriate level of activin signaling may be required for GSIS in pancreatic β cells, and that activin signaling involves modulation of K_ATP channel activity.     

Overexpression of a modified human malonyl-CoA decarboxylase blocks the glucose-induced increase in malonyl-CoA level but has no impact on insulin secretion in INS-1-derived (832/13) beta-cells

The long-chain acyl-CoA (LC-CoA) model of glucose-stimulated insulin secretion (GSIS) holds that secretion is linked to a glucose-induced increase in malonyl-CoA level and accumulation of LC-CoA in the cytosol. We have previously tested the validity of this proposal by overexpressing goose malonyl-CoA decarboxylase (MCD) in INS-1 cells, but these studies have been criticized due to: 1) the small insulin secretion response (2-4-fold) of the INS-1 cells used; 2) unknown contribution of the ATP-sensitive K(+) (K(ATP)) channel-independent pathway of GSIS in INS-1 cells, which has been implicated as the site at which lipids regulate insulin granule exocytosis; and 3) deletion of the N-terminal mitochondrial targeting sequence, but not the C-terminal peroxisomal targeting sequence in the goose MCD construct, raising the possibility that a significant fraction of the overexpressed enzyme was localized to peroxisomes. To address these outstanding concerns, INS-1-derived 832/13 cells, which exhibit robust K(ATP) channel-dependent and -independent pathways of GSIS, were treated with a new adenovirus encoding human MCD lacking both its mitochondrial and peroxisomal targeting sequences (AdCMV-MCD Delta 5), resulting in large increases in cytosolic MCD activity. Treatment of 832/13 cells with AdCMV-MCD Delta 5 completely blocked the glucose-induced rise in malonyl-CoA and attenuated the inhibitory effect of glucose on fatty acid oxidation. However, MCD overexpression had no effect on K(ATP) channel-dependent or -independent GSIS in 832/13 cells. Furthermore, combined treatment of 832/13 cells with AdCMV-MCD Delta 5 and triacsin C, an inhibitor of long chain acyl-CoA synthetase that reduces LC-CoA levels, did not impair GSIS. These findings extend our previous observations and are not consistent with the LC-CoA hypothesis as originally set forth.     

A unique allosteric insulin receptor monoclonal antibody that prevents hypoglycemia in the SUR-1−/− mouse model of KATP hyperinsulinism

Loss-of-function mutations of the ß-cell ATP-sensitive potassium channels (K_ATP) cause the most common and severe form of congenital hyperinsulinism (K_ATPHI), a disorder of ß-cell function characterized by severe hypoglycemia. Children with K_ATPHI are typically unresponsive to medical therapy and require pancreatectomy for intractable hypoglycemia. We tested the hypothesis that inhibition of insulin receptor signaling may prevent hypoglycemia in K_ATPHI. To test this hypothesis, we examined the effect of an antibody allosteric inhibitor of the insulin receptor, XMetD, on fasting plasma glucose in a mouse model of K_ATPHI (SUR-1^{? / ?} mice). SUR-1^{? / ?} and wild-type mice received twice weekly intraperitoneal injections of either XMetD or control antibody for 8 wks. Treatment with XMetD significantly decreased insulin sensitivity, and increased hepatic glucose output and fasting plasma glucose. These findings support the potential use of insulin receptor antagonists as a therapeutic approach to control the hypoglycemia in congenital hyperinsulinism.     

The PLC/PKC/Ras/MEK/Kv channel pathway is involved in uncarboxylated osteocalcin-regulated insulin secretion in rats

Uncarboxylated osteocalcin, a bone matrix protein, has been proposed to regulate glucose metabolism by increasing insulin secretion, improving insulin sensitivity and stimulating β cell proliferation. Our previous study also indicated that uncarboxylated osteocalcin stimulates insulin secretion by inhibiting voltage-gated potassium (K_V) channels. The goal of this study is to further investigate the underlying mechanisms for the regulation of Kv channels and insulin secretion by uncarboxylated osteocalcin. Insulin secretion and Kv channel currents were examined by radioimmunoassay and patch-clamp technique, respectively. Calcium imaging system was applied to measure intracellular Ca²⁺ concentration ([Ca²⁺]_i). The protein levels were detected by western blot. The results showed that uncarboxylated osteocalcin potentiated insulin secretion, inhibited Kv channels and increased [Ca²⁺]_i compared to control. These effects were suppressed by phospholipase-C (PLC)/protein kinase C (PKC)/Ras/MAPK-ERK kinase (MEK) signaling pathway, indicating that this signaling pathway plays an important role in uncarboxylated osteocalcin-regulated insulinotropic effect. In addition, the results also showed that adenylyl cyclase (AC) did not influence the effect of uncarboxylated osteocalcin on insulin secretion and Kv channels, suggesting that AC is not involved in uncarboxylated osteocalcin-stimulated insulin secretion. These findings provide new insight into the mechanism of uncarboxylated osteocalcin-regulated insulin secretion.     

Critical Role of Gap Junction Coupled KATP Channel Activity for Regulated Insulin Secretion

Pancreatic β-cells secrete insulin in response to closure of ATP-sensitive K⁺ (K_ATP) channels, which causes membrane depolarization and a concomitant rise in intracellular Ca²⁺ (Ca_i). In intact islets, β-cells are coupled by gap junctions, which are proposed to synchronize electrical activity and Ca_i oscillations after exposure to stimulatory glucose (>7 mM). To determine the significance of this coupling in regulating insulin secretion, we examined islets and β-cells from transgenic mice that express zero functional K_ATP channels in approximately 70% of their β-cells, but normal K_ATP channel density in the remainder. We found that K_ATP channel activity from approximately 30% of the β-cells is sufficient to maintain strong glucose dependence of metabolism, Ca_i, membrane potential, and insulin secretion from intact islets, but that glucose dependence is lost in isolated transgenic cells. Further, inhibition of gap junctions caused loss of glucose sensitivity specifically in transgenic islets. These data demonstrate a critical role of gap junctional coupling of K_ATP channel activity in control of membrane potential across the islet. Control via coupling lessens the effects of cell–cell variation and provides resistance to defects in excitability that would otherwise lead to a profound diabetic state, such as occurs in persistent neonatal diabetes mellitus.     

HERG1 Currents in Native K562 Leukemic Cells

The human ether-a-go-go related gene (HERG1) K⁺ channel is expressed in neoplastic cells, in which it was proposed to play a role in proliferation, differentiation and/or apoptosis. K562 cells (a chronic myeloid leukemic human cell line) express both the full-length (herg1a) and the N-terminally truncated (herg1b) isoforms of the gene, and this was confirmed with Western blots and coimmunoprecipitation experiments. Whole-cell currents were studied with a tail protocol. Seventy-eight percent of cells showed a HERG1-like current: repolarization to voltages negative to −40 mV produced a transient peak inward tail current, characteristic of HERG1 channels. Cells were exposed to a HERG-specific channel blocker, E4031. Half-maximal inhibitory concentration (IC₅₀) of the blocker was 4.69 nm. The kinetics of the HERG1 current in K562 cells resembled the rapid component of the native cardiac delayed rectifier current, known to be conducted by heterotetrameric HERG1 channels. Fast and slow deactivation time constants at −120 mV were 27.5 and 239.5 ms, respectively. Our results in K562 cells suggest the assembling of heterotetrameric channels, with some parameters being dominated by one of the isoforms and other parameters being intermediate. Hydrogen peroxide was shown to increase HERG1a K⁺ current in heterologous expression systems, which constitutes an apoptotic signal. However, we found that K562 HERG1 whole-cell currents were not activated by H₂O₂.     

Differential effects of propofol and isoflurane on glucose utilization and insulin secretion

AimsVolatile anesthetics, such as isoflurane, reverse glucose-induced inhibition of pancreatic adenosine triphosphate-sensitive potassium (K_ATP) channel activity, resulting in reduced insulin secretion and impaired glucose tolerance. No previous studies have investigated the effects of intravenous anesthetics, such as propofol, on pancreatic K_ATP channels. We investigated the cellular mechanisms underlying the effects of isoflurane and propofol on pancreatic K_ATP channels and insulin secretion.Main methodsIntravenous glucose tolerance tests (IVGTT) were performed on male rabbits. Pancreatic islets were isolated from male rats and used for a perifusion study, measurement of intracellular ATP concentration ([ATP]_i), and patch clamp experiments.Key findingsGlucose stimulus significantly increased insulin secretion during propofol anesthesia, but not isoflurane anesthesia, in IVGTT study. In perifusion experiments, both islets exposed to propofol and control islets not exposed to anesthetic had a biphasic insulin secretory response to a high dose of glucose. However, isoflurane markedly inhibited glucose-induced insulin secretion. In a patch clamp study, the relationship between ATP concentration and channel activity could be fitted by the Hill equation with a half-maximal inhibition of 22.4, 15.8, and 218.8 μM in the absence of anesthetic, and with propofol, and isoflurane, respectively. [ATP]_i and single K_ATP channel conductance did not differ in islets exposed to isoflurane or propofol.SignificanceOur results indicate that isoflurane, but not propofol, decreases the ATP sensitivity of K_ATP channels and impairs glucose-stimulated insulin release. These differential actions of isoflurane and propofol on ATP sensitivity may explain the differential effects of isoflurane and propofol on insulin release.     

Modeling K(ATP) channel gating and its regulation

ATP-sensitive potassium (K_ATP) channels couple cell metabolism to plasmalemmal potassium fluxes in a variety of cell types. The activity of these channels is primarily determined by intracellular adenosine nucleotides, which have both inhibitory and stimulatory effects. The role of K_ATP channels has been studied most extensively in pancreatic beta-cells, where they link glucose metabolism to insulin secretion. Many mutations in K_ATP channel subunits (Kir6.2, SUR1) have been identified that cause either neonatal diabetes or congenital hyperinsulinism. Thus, a mechanistic understanding of K_ATP channel behavior is necessary for modeling beta-cell electrical activity and insulin release in both health and disease. Here, we review recent advances in the K_ATP channel structure and function. We focus on the molecular mechanisms of K_ATP channel gating by adenosine nucleotides, phospholipids and sulphonylureas and consider the advantages and limitations of various mathematical models of macroscopic and single-channel K_ATP currents. Finally, we outline future directions for the development of more realistic models of K_ATP channel gating.     

Molecular determinants of ATP-sensitive potassium channel MgATPase activity: diabetes risk variants and diazoxide sensitivity

ATP-sensitive K⁺ (K_ATP) channels play an important role in insulin secretion. K_ATP channels possess intrinsic MgATPase activity that is important in regulating channel activity in response to metabolic changes, although the precise structural determinants are not clearly understood. Furthermore, the sulfonylurea receptor 1 (SUR1) S1369A diabetes risk variant increases MgATPase activity, but the molecular mechanisms remain to be determined. Therefore, we hypothesized that residue–residue interactions between 1369 and 1372, predicted from in silico modelling, influence MgATPase activity, as well as sensitivity to the clinically used drug diazoxide that is known to increase MgATPase activity. We employed a point mutagenic approach with patch-clamp and direct biochemical assays to determine interaction between residues 1369 and 1372. Mutations in residues 1369 and 1372 predicted to decrease the residue interaction elicited a significant increase in MgATPase activity, whereas mutations predicted to possess similar residue interactions to wild-type (WT) channels elicited no alterations in MgATPase activity. In contrast, mutations that were predicted to increase residue interactions resulted in significant decreases in MgATPase activity. We also determined that a single S1369K substitution in SUR1 caused MgATPase activity and diazoxide pharmacological profiles to resemble those of channels containing the SUR2A subunit isoform. Our results provide evidence, at the single residue level, for a molecular mechanism that may underlie the association of the S1369A variant with type 2 diabetes. We also show a single amino acid difference can account for the markedly different diazoxide sensitivities between channels containing either the SUR1 or SUR2A subunit isoforms.     

Diadenosine tetraphosphate-gating of recombinant pancreatic ATP-sensitive K(+) channels

Diadenosine tetraphosphate (Ap4A) has been recently discovered in the pancreatic cells where targets ATP-sensitive K⁺ (K_ATP) channels, depolarizes the cell membrane and induces insulin secretion. However, whether Ap4A inhibit pancreatic K_ATP channels by targeting protein channel complex itself was unknown. Therefore, we coexpressed pancreatic KATP channel subunits, Kir6.2 and SUR1, in COS-7 cells and examined the effect of Ap4A on the single channel behavior using the inside-out configuration of the patch-clamp technique. Ap4A inhibited channel opening in a concentration-dependent manner. Analysis of single channels demonstrated that Ap4A did not change intraburst kinetic behavior of K_ATP channels, but rather decreased burst duration and increased between-burst duration. It is concluded that Ap4A antagonizes K_ATP channel opening by targeting channel subunits themselves and by keeping channels longer in closed interburst states.     

Nesfatin-1 inhibits voltage gated K+ channels in pancreatic beta cells

The anorexigenic neuropeptide NEFA/nucleobindin 2 (NUCB2)/nesfatin-1-containing neurons are distributed in the brain regions involved in feeding regulation. In spite of the growing knowledge of its physiological functions through extensive studies, its molecular mechanism of reaction, including its receptor, remains unknown. NUCB2/nesfatin-1 is also involved in various peripheral regulations, including glucose homeostasis. In pancreatic beta-cells, NUCB2/nesfatin-1 is reported to enhance glucose-stimulated insulin secretion (GSIS) but its exact mechanism remains unknown.To clarify this mechanism, we measured the effect of nesfatin-1 on the electrical activity of pancreatic beta-cells. Using mouse primary beta cells, we measured changes in the ATP-sensitive K⁺ (K_ATP) channel current, the voltage-gated K⁺ (Kv) channel current, and insulin secretion upon application of nesfatin-1.Nesfatin-1 inhibited the Kv channel, but K_ATP channel activity was unaffected. Nesfatin-1 enhanced insulin secretion to a same level as Kv channel blocker tetraethylammonium (TEA). The effect was not further enhanced when nesfatin-1 and TEA were applied simultaneously. The inhibition binding assay with [¹²⁵I]nesfatin-1 in Kv2.1 channels, major contributor of Kv current in beta cell, expressing HEK239 cells indicated the binding of nesfatin-1 on Kv2.1 channel.Because Kv channel inhibition enhances insulin secretion under high glucose conditions, our present data suggest a possible mechanism of nesfatin-1 on enhancing GSIS through regulation of ion channels rather than its unidentified receptor.     

多不饱和脂肪酸对钾通道的调控作用及机理

多不饱和脂肪酸具有包括离子通道在内的众多作用靶点,通过作用于这些靶点,可以有效保护免疫系统、神经系统和心血管系统的功能,在一定程度上保护人体健康。电压门控钾离子通道家族K_V7通道和大电导钙离子激活的钾离子通道(BK_Ca)广泛表达于机体的各类组织中,具有重要的生理或病理功能。本综述围绕K_V7和BK_Ca通道,根据对已有报道的汇总,多不饱和脂肪酸可以增大K_V7和BK_Ca通道的电流幅值,其中对K_V7通道电流的影响主要是改变其电压依赖特性和最大电导值,而对BK_Ca通道电流的影响主要是改变其孔道区域关闭态的构象。此外,多不饱和脂肪酸对K_V7和BK_Ca通道功能的调节也会受到共表达的辅助亚基影响,但相关机制有待进一步阐明。深入理解多不饱和脂肪酸对K_V7和BK_Ca通道调节作用效果和分子机制,有助于全面理解K_V7和BK