Subunit Of ATP-sensitive Potassium Channel Research Articles

Differential roles for SUR subunits in KATP channel membrane targeting and regulation

since their discovery over 25 years ago, ATP-sensitive K+ (KATP) channels have been studied extensively in many tissues, including heart, pancreas, brain, skeletal and smooth muscle, pituitary, and kidney ([6][1], [10][2], [18][3], [19][4]). KATP channels are critical sensors that couple cellular

The mitochondrial bioenergetic phenotype for protection from cardiac ischemia in SUR2 mutant mice

The sulfonylurea receptor-2 (SUR2) is a subunit of ATP-sensitive potassium channels (K(ATP)) in heart. Mice with the SUR2 gene disrupted (SUR2m) are constitutively protected from ischemia-reperfusion (I/R) cardiac injury. This was surprising because K(ATP), either sarcolemmal or mitochondrial or both, are thought to be important for cardioprotection. We hypothesized that SUR2m mice have an altered mitochondrial phenotype that protects against I/R. Mitochondrial membrane potential (ΔΨ(m)), tolerance to Ca(2+) load, and reactive oxygen species (ROS) generation were studied by fluorescence-based assays, and volumetric changes in response to K(+) were measured by light scattering in isolated mitochondria. For resting SUR2m mitochondria compared with wild type, the ΔΨ(m) was less polarized (46.1 ± 0.4 vs. 51.9 ± 0.6%), tolerance to Ca(2+) loading was increased (163 ± 2 vs. 116 ± 2 μM), and ROS generation was enhanced with complex I [8.5 ± 1.2 vs. 4.9 ± 0.2 arbitrary fluorescence units (afu)/s] or complex II (351 ± 51.3 vs. 166 ± 36.2 afu/s) substrates. SUR2m mitochondria had greater swelling in K(+) medium (30.2 ± 3.1%) compared with wild type (14.5 ± 0.6%), indicating greater K(+) influx. Additionally, ΔΨ(m) decreased and swelling increased in the absence of ATP in SUR2m, but the sensitivity to ATP was less compared with wild type. When the mitochondria were subjected to hypoxia-reoxygenation, the decrease in respiration rates and respiratory control index was less in SUR2m. ΔΨ(m) maintenance in the SUR2m intact myocytes was also more tolerant to metabolic inhibition. In conclusion, the cardioprotection observed in the SUR2m mice is associated with a protected mitochondrial phenotype resulting from enhanced K(+) conductance that partially dissipated ΔΨ(m). These results have implications for possible SUR2 participation in mitochondrial K(ATP).

Effects of Guanxinkang on expressions of ATP-sensitive potassium channel subunits Kir6.1, Kir6.2, SUR2A and SUR2B in ischemic myocytes of rats

To observe the effects of Guanxinkang injection, a compound traditional Chinese herbal medicine, on ATP-sensitive potassium (K(ATP)) channel subunits in ischemic myocardial cells of rats, and to explore the mechanism of Guanxinkang in protecting myocardial ischemic reperfusion injuries. Forty-eight Wistar rats were randomly divided into normal group, untreated group, glibenclamide group, pinacidil group, Guanxinkang group and Guanxinkang plus glibenclamide group. The ventricular myocytes were prepared from hearts of normal rats by enzymatic dissociation method. The ischemic ventricular myocytes underwent perfusion with normal Tyrode solution for 10 min, then stopping perfusion 30 min, and followed by 45 min of reperfusion. The glibenclamide, pinacidil and Guanxinkang were added into ventricular myocytes solution directly. Then the solutions were placed at 4 degrees centigrade. After 24-hour freezing at -80 degrees centigrade, mRNA and protein expressions of KATP subunits Kir6.1, Kir6.2, SUR2A and SUR2B were measured by real-time quantitative polymerase chain reaction and Western blotting respectively. In normal rat myocardial cells, there were SUR2A, Kir6.1, and Kir6.2 protein and gene expressions but no expression of SUR2B protein. In the untreated group, all subunit mRNA and protein expressions of KATP increased to some extent as compared with the normal group. Pinacidil, a potassium channel opener, significantly increased mRNA and protein expressions of KATP subunits, while the blocker glibenclamide had a reverse effect. Meanwhile, Guanxinkang injection significantly increased mRNA and protein expressions of K(ATP) subunits but with no significant difference as compared with pinacidil. Guanxinkang injection can obviously enhance the open of KATP channel and thus play a role in cardiovascular protection.

New Uses for Old Drugs: Neonatal Diabetes and Sulphonylureas

The discovery that their neonatal diabetes is caused by gain-of-function mutations in the K(ATP) channel has enabled many patients to switch from insulin to oral sulphonylurea drugs. Here, I review molecular, physiological, and clinical features of this change in therapy.

Definition, epidemiology and classification of diabetes in children and adolescents

Diabetes mellitus is a group of metabolic diseases characterised by chronic hyperglycemia resulting from defects in insulin secretion, insulin action, or both. The abnormalities in carbohydrate, fat, and protein metabolism that are found in diabetes are due to deficient action of insulin on target tissues. If ketones are present in blood or urine, treatment is urgent, because ketoacidosis can evolve rapidly.

Exchange protein activated by cAMP (Epac) mediates cAMP‐dependent but protein kinase A‐insensitive modulation of vascular ATP‐sensitive potassium channels

Exchange proteins directly activated by cyclic AMP (Epacs or cAMP-GEF) represent a family of novel cAMP-binding effector proteins. The identification of Epacs and the recent development of pharmacological tools that discriminate between cAMP-mediated pathways have revealed previously unrecognized roles for cAMP that are independent of its traditional target cAMP-dependent protein kinase (PKA). Here we show that Epac exists in a complex with vascular ATP-sensitive potassium (KATP) channel subunits and that cAMP-mediated activation of Epac modulates KATP channel activity via a Ca2+-dependent mechanism involving the activation of Ca2+-sensitive protein phosphatase 2B (PP-2B, calcineurin). Application of the Epac-specific cAMP analogue 8-pCPT-2'-O-Me-cAMP, at concentrations that activate Epac but not PKA, caused a 41.6 +/- 4.7% inhibition (mean +/- S.E.M.; n = 7) of pinacidil-evoked whole-cell KATP currents recorded in isolated rat aortic smooth muscle cells. Importantly, similar results were obtained when cAMP was elevated by addition of the adenylyl cyclase activator forskolin in the presence of the structurally distinct PKA inhibitors, Rp-cAMPS or KT5720. Activation of Epac by 8-pCPT-2'-O-Me-cAMP caused a transient 171.0 +/- 18.0 nM (n = 5) increase in intracellular Ca2+ in Fura-2-loaded aortic myocytes, which persisted in the absence of extracellular Ca2+. Inclusion of the Ca2+-specific chelator BAPTA in the pipette-filling solution or preincubation with the calcineurin inhibitors, cyclosporin A or ascomycin, significantly reduced the ability of 8-pCPT-2'-O-Me-cAMP to inhibit whole-cell KATP currents. These results highlight a previously undescribed cAMP-dependent regulatory mechanism that may be essential for understanding the physiological and pathophysiological roles ascribed to arterial KATP channels in the control of vascular tone and blood flow.

Mutations in the ABCC8 gene encoding the SUR1 subunit of the KATP channel cause transient neonatal diabetes, permanent neonatal diabetes or permanent diabetes diagnosed outside the neonatal period

Mutations in the ABCC8 gene encoding the SUR1 subunit of the pancreatic ATP-sensitive potassium channel cause permanent neonatal diabetes mellitus (PNDM) and transient neonatal diabetes mellitus (TNDM). We reviewed the existing literature, extended the number of cases and explored genotype-phenotype correlations. Mutations were identified by sequencing in patients diagnosed with diabetes before 6 months without a KCNJ11 mutation. We identified ABCC8 mutations in an additional nine probands (including five novel mutations L135P, R306H, R1314H, L438F and M1290V), bringing the total of reported families to 48. Both dominant and recessive mutations were observed with recessive inheritance more common in PNDM than TNDM (9 vs. 1; p < 0.01). The remainder of the PNDM probands (n = 12) had de novo mutations. Seventeen of twenty-five children with TNDM inherited their heterozygous mutation from a parent. Nine of these parents had permanent diabetes (median age at diagnosis: 27.5 years, range: 13-35 years). Recurrent mutations of residues R1183 and R1380 were found only in TNDM probands and dominant mutations causing PNDM clustered within exons 2-5. ABCC8 mutations cause PNDM, TNDM or permanent diabetes diagnosed outside the neonatal period. There is some evidence that the location of the mutation is correlated with the clinical phenotype.

Challenges in studies of the genetic basis of Type 2 diabetes

The prevalence of diabetes is increasing worldwide in epidemic proportions. This increase is mainly due to increased incidence and prevalence of Type 2 diabetes, which accounts for 80–90% of all cases of diabetes. The susceptibility to develop Type 2 diabetes is determined by genetic and environmental factors. Major genes responsible for Type 2 diabetes have not yet been identified. The most replicated susceptibility gene for Type 2 diabetes is TCF7L2, recently published by investigators from Iceland. The second most widely replicated association between a genetic variation and the risk of Type 2 diabetes is that of the Pro12Ala polymorphism in the peroxisome proliferator-activated receptor γ2 gene. Furthermore, the common E23K polymorphism in the KCJN11 gene, encoding the ATP-sensitive potassium-channel subunit Kir6.2, and variants in the calpain-10 gene have been associated with increased susceptibility to Type 2 diabetes in meta-analyses. Several studies have investigated the possibility that rare, highly penetrant mutations in the maturity-onset diabetes of the young genes lead to monogenic diabetes, while common polymorphisms increase the susceptibility to Type 2 diabetes. Indeed, there is increasing evidence that single nucleotide polymorphisms in hepatic nuclear factor-4α are significantly associated with the risk of Type 2 diabetes. In this review, different approaches to identify susceptibility genes for Type 2 diabetes are discussed. In particular, the importance of prospective population-based cohort studies and prospective intervention studies are emphasized. Finally, genome-wide association studies using single nucleotide polymorphisms randomly spaced across the entire genome may be useful in the identification of susceptibility genes for Type 2 diabetes.

Pharmacological and molecular characterization of ATP-sensitive K + conductances in CART and NPY/AgRP expressing neurons of the hypothalamic arcuate nucleus

The role of hypothalamic ATP-sensitive potassium channels in the maintenance of energy homeostasis has been extensively explored. However, how these channels are incorporated into the neuronal networks of the arcuate nucleus remains unclear. Whole-cell patch-clamp recordings from rat arcuate nucleus neurons in hypothalamic slice preparations revealed widespread expression of functional ATP-sensitive potassium channels within the nucleus. ATP-sensitive potassium channels were expressed in orexigenic neuropeptide Y/agouti-related protein (NPY/AgRP) and ghrelin-sensitive neurons and in anorexigenic cocaine-and-amphetamine regulated transcript (CART) neurons. In 70% of the arcuate nucleus neurons recorded, exposure to glucose-free bathing medium induced inhibition of electrical excitability, the response being characterized by membrane hyperpolarization, a reduction in neuronal input resistance and a reversal potential consistent with opening of potassium channels. These effects were reversible upon re-introduction of glucose to the bathing medium or upon exposure to the ATP-sensitive potassium channel blockers tolbutamide or glibenclamide. The potassium channel opener diazoxide, but not pinacidil, also induced a tolbutamide and glibenclamide-sensitive inhibition of electrical excitability. Single-cell reverse transcription–polymerase chain reaction revealed expression of mRNA for sulfonylurea receptor 1 but not sulfonylurea receptor 2 subunits of ATP-sensitive potassium channels. Thus, rat arcuate nucleus neurons, including those involved in functionally antagonistic orexigenic and anorexigenic pathways express functional ATP-sensitive potassium channels which include sulfonylurea receptor 1 subunits. These data indicate a crucial role for these ion channels in central sensing of metabolic and energy status. However, further studies are needed to clarify the differential roles of these channels, the organization of signaling pathways that regulate them and how they operate in functionally opposing cell types.

Sulfonylurea treatment outweighs insulin therapy in short-term metabolic control of patients with permanent neonatal diabetes mellitus due to activating mutations of the KCNJ11 (KIR6.2) gene

To the Editor, Activating missense mutations in the gene encoding potassium inwardly rectifying channel, subfamily J, member 11 (KCNJ11) represent the most common cause (40 to 64%, depending on populations) of permanent neonatal diabetes mellitus in patients diagnosed in the first 6 months of life [1, 2]. In addition, KCNJ11 activating mutations can lead to transient/relapsing neonatal diabetes [3, 4]. The KCNJ11 gene encodes the pore-forming subunit (also known as KIR6.2) of the pancreatic beta cell ATP-sensitive potassium channel (KATP), which exerts a pivotal role in glucose-regulated insulin release. In the beta cell, KIR6.2 forms a hetero-octameric complex (4:4) with the sulfonylurea receptor subtype 1 (SUR1); binding to SUR1 by sulfonylureas determines channel closure and insulin secretion [2]. In previously published cases, seven patients have been reported to respond well to the transfer from insulin to oral hypoglycaemic agents [4–8]. Here we report on the replacement of insulin with sulfonylureas in ten Italian children who have mutations in KCNJ11 (R50P, V59M [x4], K170R, R201C and R201H [x3]) and were followed in nine Diabetologia (2006) 49:2210–2213 DOI 10.1007/s00125-006-0329-x

KCNJ11 activating mutations are associated with developmental delay, epilepsy and neonatal diabetes syndrome and other neurological features

Heterozygous activating mutations in the gene encoding for the ATP-sensitive potassium channel subunit Kir6.2 (KCNJ11) have recently been shown to be a common cause of permanent neonatal diabetes. Kir6.2 is expressed in muscle, neuron and brain as well as the pancreatic beta-cell, so patients with KCNJ11 mutations could have a neurological phenotype in addition to their diabetes. It is proposed that some patients with KCNJ11 mutations have neurological features that are part of a discrete neurological syndrome termed developmental Delay, Epilepsy and Neonatal Diabetes (DEND), but there are also neurological consequences of chronic or acute diabetes. We identified KCNJ11 mutations in four of 10 probands with permanent neonatal diabetes and one affected parent; this included the novel C166F mutation and the previously described V59M and R201H. Four of the five patients with mutations had neurological features: the patient with the C166F mutation had marked developmental delay, severe generalised epilepsy, hypotonia and muscle weakness; mild developmental delay was present in the patient with the V59M mutation; one patient with the R201H mutation had acute and chronic neurological consequences of cerebral oedema and another had diabetic neuropathy from chronic hyperglycaemia. In conclusion, the clinical features in these patients support the existence of a discrete neurological syndrome with KCNJ11 mutations. The severe DEND syndrome was seen with the novel C166F mutation and mild developmental delay with the V59M mutation. These features differ markedly from the neurological consequences of acute or chronic diabetes.

Mutations in KCNJ11, which encodes Kir6.2, are a common cause of diabetes diagnosed in the first 6 months of life, with the phenotype determined by genotype

Heterozygous activating mutations in KCNJ11, which encodes the Kir6.2 subunit of the pancreatic ATP-sensitive potassium (K(ATP)) channel, cause both permanent and transient neonatal diabetes. A minority of patients also have neurological features. The identification of a KCNJ11 mutation has important therapeutic implications, as many patients can replace insulin injections with sulfonylurea tablets. We aimed to determine the age of presentation of patients with KCNJ11 mutations and to examine if there was a relationship between genotype and phenotype. KCNJ11 was sequenced in 239 unrelated patients from 21 countries, who were diagnosed with permanent diabetes before 2 years of age. Thirty-one of the 120 patients (26%) diagnosed in the first 26 weeks of life had a KCNJ11 mutation; no mutations were found in the 119 cases (0%) diagnosed after this age. Fourteen different heterozygous mutations were identified, with the majority resulting from de novo mutations. These include seven novel mutations: H46Y, R50Q, G53D C166Y, K170T, L164P and Y330S. All 11 probands with the most common mutation, R201H, had isolated diabetes. In contrast, developmental delay in addition to diabetes was seen in four of five probands with the V59M mutation and two of four with the R201C mutation. Five patients with developmental delay, epilepsy and neonatal diabetes (DEND) syndrome had unique mutations not associated with other phenotypes. KCNJ11 mutations are a common cause of permanent diabetes diagnosed in the first 6 months and all patients diagnosed in this age group should be tested. There is a strong genotype-phenotype relationship with the mutation being an important determinant of associated neurological features.

A New Insight Into the Pathogenesis of Coronary Vasospasm

See related article, pages 682–689 To elucidate the control mechanisms of coronary vascular tone is one of the central interests in cardiac pathophysiology, because ischemic heart disease is one of the major causes of death in many countries. Although the coronary vascular tone is finally determined by the contractile state of smooth muscle, exo-smooth muscle mechanisms including autonomic nerves, endothelial cells, and blood cells have been shown indispensable for the control. Particular types of receptors, ion channels, and intracellular signal-cascades exist in coronary smooth muscle cells and mediate the controls by exo-smooth muscle elements (Figure). For example, stimulation of α1-adrenergic receptor, which is physiologically achieved by noradrenaline (NA) released from sympathetic presynapses, increases the intracellular Ca2+ (Ca2+i) via phosphatidylinositol (PI)-turnover and also probably via opening of receptor-activated Ca2+-permeable TRP channel. Membrane depolarization does so via opening voltage-dependent Ca2+ channels. The augmentation of Ca2+i results in contraction of the smooth muscle cells and thus constriction of the coronary artery.1 Activation of β2-adrenergic receptor, in turn, inhibits the coronary smooth muscle contraction through protein-kinase A pathway.2 The contraction is also suppressed by protein-kinase G activated by a dilating factor, nitric oxide (NO), which is produced in the endothelial cells. The mechanism for control of vascular tone . Activation of voltage-gated Ca2+ channel at the presynapse of sympathetic nerve increases intracellular Ca2+, which triggers a release of norepinephrine (NE). NE stimulates adrenergic α1 receptor (α1R) in the smooth muscle cells and drives PI-turnover as described in this scheme. The intracellular Ca2+, which flows into the cells via smooth-muscle’s Ca2+ channel or moves from endoplasmic reticulum (ER), contracts the cells. The constriction of smooth muscle cells is prevented by activation …

The E23K polymorphism in Kir6.2 gene and coronary heart disease

Background The G to A mutation in the Kir 6.2, the ATP-sensitive potassium channel subunit, resulted a glutamate (E) to lysine (K) substitution at codon 23, and the A allele was shown to have a relationship with high risk to type 2 diabetes in previous study. Their role in coronary heart disease (CHD) has not been evaluated. We hypothesized that the polymorphism would be associated with increased susceptibility to CHD. Methods The E23K gene polymorphism of Kir6.2 gene was analyzed by PCR-restriction site polymorphism (PCR-RSP) methods in 101 controls and 119 CHD patients. Serum lipids and C reactive protein concentrations were measured in all subjects. Results Among the CHD patients, the frequency of the G allele was higher (63.4% vs. 56.9%, P > 0.05) and the frequency of the A allele was lower (36.6% vs. 43.1%, P > 0.05) than among controls. No significant differences were found in allele frequencies between CHD and controls ( P > 0.05), but there were significant differences in GG and combined (GA + AA) genotypes frequencies (42.0% vs. 28.7%, and 58.0% vs. 71.3%, P < 0.050). Conclusions The E23K gene polymorphism in Kir6.2 gene appeared to be related to high susceptibility to CHD.

Assessment of Insulin Sensitivity in Adults with Permanent Neonatal Diabetes Mellitus due to Mutations in the KCNJ11 Gene Encoding Kir6.2

Activating mutations in the KCNJ11 gene encoding the Kir6.2 subunit of ATP-sensitive potassium channel have been described in patients with permanent neonatal diabetes mellitus (PNDM). The main pathophysiological feature of PNDM associated with Kir6.2 mutations is a profound defect in insulin secretion. However, the expression of Kir6.2 protein is not limited to beta-cells; it also includes skeletal muscles, heart, brain, and peripheral nerves. Thus, the hypothesis that Kir6.2 mutations may influence insulin sensitivity in humans seems justified. Moreover, this notion is additionally supported by an animal model of Kir6.2 knock-out mice. Four adult carriers of a Kir6.2 mutation from the Polish population (mean age 31.5 years, range 20-50) were available for this study that aimed to evaluate their insulin sensitivity by the hyperinsulinemic euglycemic clamp technique. Three subjects carried the R201H mutation and one patient was a carrier of the K170N mutation. In addition, eight healthy volunteers with normal glucose tolerance were examined for comparison (mean age 31.0 years, range 20-41). The mean M value, i.e. the amount of metabolized glucose, for PNDM cases equaled 4.49 mg/(kg x min) (range 2.76-6.66) and was significantly lower than in the control group (9.64 mg/(kg x min), range 4.59-18.00). This observation suggests that impaired insulin sensitivity, in addition to profoundly decreased insulin secretion, contributes to the clinical picture of PNDM resulting from mutations in the Kir6.2 gene. An additional factor that might influence insulin sensitivity in our diabetes patients is glucose toxicity that may have appeared due to poor metabolic control prior to the examination (mean HbA1c = 8.95%). The intriguing question to be answered in the future is whether an improvement in insulin action could be seen following the transfer of Kir6.2 mutation carriers to sulphonylurea compounds.

A New ATP-Sensitive Potassium Channel Opener Protects the Kidney from Hypertensive Damage in Spontaneously Hypertensive Rats

The effects of iptakalim, a new ATP-sensitive potassium channel opener, were studied in spontaneously hypertensive rats (SHR). Treatment of 12-week-old male SHR (six animals in each group) with iptakalim by gastric lavage at doses of 1, 3, or 9 mg/kg/day for 12 weeks resulted in a lowering of blood pressure. Iptakalim provided significant renoprotection to SHR rats as measured by decreased proteinuria and improved renal function. Histological evidence demonstrated that iptakalim could reverse renal vascular remodeling (of afferent arterioles, arcuate arteries, or interlobular arteries), and improve pathological changes of glomerular, renal interstitial, and glomerular filtration membranes. These effects were accompanied by the decreased circulation and intrarenal concentrations of endothelin 1 and transforming growth factor beta1 (TGF-beta1), and down-regulated overexpression of genes for ET-1, endothelin-converting enzyme 1, TGF-beta1, and the subunits of ATP-sensitive potassium channels (K(ATP)), Kir1.1 and Kir6.1, in the kidney during hypertension. Abnormal expression of matrix components [collagen IV, fibronectin, matrix metalloproteinase 9 (MMP-9) and MMP tissue inhibitor 1 (TIMP-1)] was also significantly reversed by iptakalim. Our results demonstrate that chronic treatment with iptakalim not only reduces blood pressure but also preserves renal structure and function in SHR. In addition to reducing blood pressure, the renoprotective of iptakalim may be involved in inhibiting the circulation and intrarenal concentrations of endothelin 1 and TGF-beta1, regulating the expression of K(ATP) genes and correcting MMP-9/TIMP-1 imbalance in renal tissue, which may result in reducing the accumulation of extracellular matrix molecules.

The identification of a R201H mutation in KCNJ11, which encodes Kir6.2, and successful transfer to sustained-release sulphonylurea therapy in a subject with neonatal diabetes: evidence for heterogeneity of beta cell function among carriers of the R201H mutation

To the Editor Diabetes caused by severe mutations in beta cell genes is usually diagnosed as neonatal diabetes [1] or MODY [2]. Activating mutations in KCJN11, the gene encoding the ATP-sensitive potassium channel subunit Kir6.2, have been described in very-early-onset diabetes ( A) was found in a single patient. This child was born at 40 weeks’ gestation and weighed 2,450 g. He was diagnosed with diabetes during the third week of life based on a plasma glucose of 35–50 mmol/l, without ketoacidosis, which was measured when he presented with pneumonia and bilateral acute otitis media. The patient was treatedwith insulin, with a dose of 0.7–1.0 U/kg used initially and subsequently decreased. At 9 years, 11 months he weighed 27.5 kg and his daily insulin requirement was 7 U (0.25 U/kg) as a single morning injection of intermediate-acting insulin. Despite little modification to his diet he rarely experienced hyperglycaemia above 11 mmol/l, and had an HbA1c level of 6.6%. These observations suggested endogenous beta cell function, which was confirmed by a fasting plasma C-peptide of 443 pmol/l (glucose 6.7 mmol/l) and an increase in plasma insulin concentration of 70 pmol/l during an IVGTT (Fig. 1). As patients with Kir6.2 diabetes may respond to sulphonylureas, we assessed whether this patient could successfully transfer to sulphonylurea tablets [3, 4]. Glipizide gastrointestinal therapeutic system (GITS), a controlledrelease sulphonylurea, was introduced [5]. A dose of 5 mg was administered for 2 days, then 10 mg; insulin was simultaneously slowly withdrawn over a period of 5 days. As the patient experienced a few mild hypoglycaemic episodes during the first 2 days after the discontinuation of insulin the glipizide GITS dose was decreased to 5 mg. While on this dose, a day profile of his capillary glucose concentrations revealed that they were between 4 and 6 mmol/l; a result confirmed by a 72-h record obtained using a continuous glucose monitoring system (Medtronic, Northridge, CA, USA). The IVGTT was repeated 3 weeks after a stable glipizide dose was achieved. At this time the patient’s fasting glucose level was 5.4mmol/l, and his C-peptide level was 347 pmol/l. T. Klupa and E. L. Edghill contributed equally to this work

The C42R Mutation in the Kir6.2 (KCNJ11) Gene as a Cause of Transient Neonatal Diabetes, Childhood Diabetes, or Later-Onset, Apparently Type 2 Diabetes Mellitus

Known genes in maturity-onset diabetes of the young account for only a fraction of families with dominantly inherited diabetes in Japan. There should be as-yet-unidentified genes that account for the rest of the patients. To identify and characterize the mutation responsible for a Japanese family with dominantly inherited diabetes mellitus. Members of a four-generation family with dominantly inherited diabetes mellitus observed in three generations. None of the patients in this family had permanent neonatal diabetes. One had transient neonatal diabetes, one had childhood diabetes, and the others had adult-onset diabetes without autoantibodies or insulin resistance. Screening of the chromosomal location of the gene by a genome-wide linkage analysis followed by candidate gene sequencing. Confirmation of the functional significance of the identified mutation by the population survey and the physiological analysis. We identified a novel mutation (C42R) in the KCNJ11 gene coding for the Kir6.2 subunit of the pancreatic ATP-sensitive potassium channel. The patch-clamp experiments using the mutated KCNJ11 showed that the mutation causes increased spontaneous open probability and reduced ATP sensitivity. The effect, however, was partially compensated by the reduction of functional ATP-sensitive potassium channel expression at the cell surface, which could account for the milder phenotype of our patients. These results broaden the spectrum of diabetes phenotypes caused by mutations of KCNJ11 and suggest that mutations in this gene should be taken into consideration for not only permanent neonatal diabetes but also other forms of diabetes with milder phenotypes and later onset.

Studies of ATP-sensitive potassium channels on 6-hydroxydopamine and haloperidol rat models of Parkinson's disease: Implications for treating Parkinson's disease?

In the present study, we first investigated the effects of unilateral 6-hydroxydopamine (6-OHDA) lesioning of the substantia nigra pars compacta (SNc) on the expression of subunits of ATP-sensitive potassium channels (KATP channels) in the prefrontal cortex (PFC), striatum and hippocampus of adult rats by utilizing semiquantitative reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemistry techniques. The results show that Kir6.2 and SUR2 expression in the PFC, Kir6.1, Kir6.2 and SUR1 expression in the striatum, and Kir6.1 and Kir6.2 expression in the hippocampus of injured side increased significantly after unilateral 6-OHDA lesioning of the SNc in rats. Afterward, we studied the effects of iptakalim (Ipt), a novel ATP-sensitive potassium channel opener (KCO), on parkinsonian symptoms, which were induced by acute injection of haloperidol. The results indicate that intraperitoneal injection of Ipt (0.125 mg/kg, 0.25 mg/kg or 0.5 mg/kg) partially alleviated haloperidol-induced catalepsy and hypolocomotion. Even though the observed effects (0.5 mg/kg) are better than those of l-3,4-dihydroxyphenylalanine ( l-DOPA) (100 mg/kg), Ipt (0.25 mg/kg) failed to enhance the anti-parkinsonian actions of l-DOPA (100 mg/kg). Our results suggest that KATP channels might be involved in the pathogenesis of Parkinson's disease (PD) induced in an animal model and conceptually support the idea that KATP channels may be new therapeutic targets for PD.

Regulation of ATP-sensitive Potassium Channel Subunit Kir6.2 Expression in Rat Intestinal Insulin-producing Progenitor Cells

We have reported that the combined expression of Pdx-1 (pancreatic duodenal homeobox 1) and Isl-1 (islet 1) enables immature rat enterocytes (IEC-6) to produce and release insulin. A key component regulating the release of insulin is the ATP-sensitive potassium channel subunit Kir6.2. To investigate the regulation of Kir6.2 gene expression, we assessed Kir6.2 expression in IEC-6 cells expressing Pdx-1 and/or Isl-1. We observed that Kir6.2 protein was expressed de novo in IEC-6 cells expressing both Pdx-1 and Isl-1 but not in cells expressing Pdx-1 alone. Next, we analyzed the regions of the Kir6.2 promoter (-1677/-45) by performing a luciferase assay and electrophoretic mobility shift assay. The results have demonstrated that Kir6.2 promoter possesses two regions regulating the promoter activity: a Foxa2-binding site (-1364 to -1210) and an Sp1/Sp3-binding site (-1035 to -939). The additional expression of Isl-1 in IEC-6 cells expressing Pdx-1 attenuated overexpression of Foxa2 protein and enhanced Kir6.2 expression. Finally, knockdown of Isl-1 using the iRNA technique resulted in decreased expression of Kir6.2 protein in a rat pancreatic beta-cell line (RIN-5F cells). These results indicate that expression of Kir6.2 in the rat intestine is moderated by Isl-1.