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Diabetes mellitus Type 2 happens to be one of the most challenging health concerns in recent times and has spiked an alarming rise taking it into epidemic category. For management of this epidemic, sulphonylureas have been cornerstone in its treatment. The inefficiency and impairment of insulin to function has been compensated by treatment with anti-hyperglycemic agents (glibenclamide). However, this has been linked with cases of hypoglycemia. In order to rectify this, the present study focuses on development of better drug analogue. Sulphonylurea receptor (SUR1) was modeled with reliable efficiency and confirmed for structural validation. The docking results were strongly supported by molecular dynamics data and molecular mechanics-generalized born surface area (MM-GBSA) calculations. Successful docking of predicted sulphonylurea receptor with designed analogue (C24H26ClN3O4S) was illustrated with stronger binding energy (− 8.3 kcal/mol) having seven hydrophobic contacts and two hydrogen bonds (Ile103and Leu116) with the receptor protein. In case of SUR1-glibenclamide complex, a binding energy of − 7.1 kcal/mol was contributed from four hydrophobic contacts and three hydrogen bonds. The predicted molecule when scrutinized for pharmacophore and QSAR properties, like polar surface area, molar refractivity, oral bioavailability, solubility, transport across the gut, resistance to blood brain barrier and intestinal absorption, showed values mostly falling in prescribed range. It also highlighted that the inhibitor is non-toxic and non-carcinogenic property. Therefore, C24H26ClN3O4S can be used as a better and potent drug for treatment of diabetes Type 2 in comparison to glibenclamide. [ABSTRACT FROM AUTHOR]

ATP-sensitive potassium (KATP) channels are a major drug target for the treatment of type-2 diabetes. KATP channels are ubiquitously expressed and link the metabolic state to electrical excitability. In pancreatic β-cells, KATP channels are crucial in the regulation of glucose-induced insulin secretion. Also, KATP channels are involved in the protection against neuronal seizures and ischaemic stress in the heart, brain and in the regulation of vascular smooth muscle tone. Functional KATP channels are hetero-octamers composed of two subunits, a pore forming Kir6, which is a member of the inwardly rectifying potassium channels family, and a regulatory sulphonylurea receptor (SUR). In response to nucleotides and pharmaceutical agonists and antagonists, SUR allosterically regulates channel gating. The allosteric communication pathways between these two heterologus proteins in KATP channels are still poorly understood. This review will highlight the therapeutic agents that target KATP channels and are used to treat diabetes and cardiovascular diseases.

Adenosine triphosphate (ATP)-sensitive potassium (KATP) channels in pancreatic β-cells play a crucial role in insulin secretion and glucose homeostasis. These channels are composed of two subunits: a pore-forming subunit (Kir6.2) and a regulatory subunit (sulphonylurea receptor-1). Recent studies identified large number of gain of function mutations in the regulatory subunit of the channel which cause neonatal diabetes. Majority of mutations cause neonatal diabetes alone, however some lead to a severe form of neonatal diabetes with associated neurological complications. This review focuses on the functional effects of these mutations as well as the implications for treatment.

Type 2 diabetes mellitus (DM2) is a chronic progressing disease associated with insulin resistance and impaired insulin secretion insufficient toovercome insulin resistance that deteriorates as a result of glucose toxicity and beta-cell apoptosis. Combination of metformin and sulfonylureas (SU) iscurrently regarded as an effective strategy of hypoglycemic therapy having effect not only on the main stages of pathogenesis but also on t dangerousrisk factors leading to adverse events (hypoglycemia, body weight increment, cardiovascular disorders). Amaryl, SU of the 3d generation, meets allcriteria of safety and efficacy for combined hypoglycemic therapy due to its high affinity to a specific subunit of SU receptors-1 on beta-cells coupled toshort-term stimulating action on insulin secretion. Moreover, it has a unique SU-unrelated extrapancreatic mechanism of action. The efficacy andsafety of Amaryl was confirmed in a number of clinical studies which gives reason to recommend it for inclusion in any modern hypoglycemic therapywith a minimal risk of hypoglycemia, lack of weight increment, positive effect on the cardiovascular system and progress of atherosclerosis

Abstract: In Type 2 Diabetes (T2D), adiponectin (AdipoQ) and sulphonylurea receptor genes (ABCC8) are important targets for candidate gene association studies. The single nucleotide polymorphisms (SNPs) in these genes have been associated with features of the metabolic syndrome across various populations. The present case–control study undertaken in the population of Punjab, evaluates the association of +45T>G polymorphism in AdipoQ gene; and Exon16-3C>T as well as Exon18C>T polymorphisms in ABCC8 gene with T2D. These SNPs were genotyped in 200 T2D cases and 200 non-diabetic healthy controls using the PCR-RFLP method. The frequency of the minor G-allele for AdipoQ+45(T>G) polymorphism was significantly higher in T2D cases (29.0%) than in controls (21.5%) [P=0.02, OR=1.49 (1.07–2.04)]. The genetic model analysis revealed that the G-allele cumulatively provides nearly 1.59–1.78 fold increased risk to T2D under the additive (P=0.009; OR=1.59, 1.12–2.25 at 95% CI), dominant (TG/GG vs. TT) (P=0.034, OR=1.64, 1.04–2.56 at 95% CI) and codominant model (TG vs. TT/GG) (P=0.014; OR=1.78, 1.12–2.82 at 95% CI) after adjusting for confounding factors. However, no difference in the distribution of genotype and allele frequencies was observed for both the ABCC8 polymorphisms. The distribution of obesity profiles (BMI, WC and WHR) was also significantly different between cases and controls (P<0.05). Higher BMI and central obesity were observed to increase the risk of T2D. G-allele of +45(T>G) polymorphism in the adiponectin gene appears to be associated with increased risk of T2D, but the polymorphisms in sulphonylurea receptor gene do not seem to be associated with T2D in the population of Punjab. [Copyright &y& Elsevier]

Adenosine triphosphate (ATP)-sensitive potassium (KATP) channels in pancreatic β-cells play a crucial role in insulin secretion and glucose homeostasis. These channels are composed of two subunits: a pore-forming subunit (Kir6.2) and a regulatory sub-unit (sulphonylurea receptor-1). Recent studies identified large number of gain of function mutations in the regulatory subunit of the channel which cause neonatal diabetes. Majority of mutations cause neonatal diabetes alone, however some lead to a severe form of neonatal diabetes with associated neurological complications. This review focuses on the functional effects of these mutations as well as the implications for treatment. [ABSTRACT FROM AUTHOR]

BACKGROUND AND PURPOSE Rosiglitazone is an anti-diabetic drug acting as an insulin sensitizer. We recently found that rosiglitazone also inhibits the vascular isoform of ATP-sensitive K+ channels and compromises vasodilatory effects of β-adrenoceptor activation and pinacidil. As its potency for the channel inhibition is in the micromolar range, rosiglitazone may be used as an effective KATP channel inhibitor for research and therapeutic purposes. Therefore, we performed experiments to determine whether other isoforms of KATP channels are also sensitive to rosiglitazone and what their sensitivities are. EXPERIMENTAL APPROACH KIR6.1/SUR2B, KIR6.2/SUR1, KIR6.2/SUR2A, KIR6.2/SUR2B and KIR6.2ΔC36 channels were expressed in HEK293 cells and were studied using patch-clamp techniques. KEY RESULTS Rosiglitazone inhibited all isoforms of KATP channels in excised patches and in the whole-cell configuration. Its IC50 was 10 µmol·L−1 for the KIR6.1/SUR2B channel and ∼45 µmol·L−1 for KIR6.2/SURx channels. Rosiglitazone also inhibited KIR6.2ΔC36 channels in the absence of the sulphonylurea receptor (SUR) subunit, with potency (IC50= 45 µmol·L−1) almost identical to that for KIR6.2/SURx channels. Single-channel kinetic analysis showed that the channel inhibition was mediated by augmentation of the long-lasting closures without affecting the channel open state and unitary conductance. In contrast, rosiglitazone had no effect on KIR1.1, KIR2.1 and KIR4.1 channels, suggesting that the channel inhibitory effect is selective for KIR6.x channels. CONCLUSIONS AND IMPLICATIONS These results suggest a novel KATP channel inhibitor that acts on the pore-forming KIR6.x subunit, affecting the channel gating. LINKED ARTICLE This article is commented on by Dart, pp. 23-25 of this issue. To view this commentary visit http://dx.doi.org/10.1111/j.1476-5381.2012.01990.x [ABSTRACT FROM AUTHOR]

Abstract: Stroke causes CNS injury associated with strong fast microglial activation as part of the inflammatory response. In rat models of stroke, sulphonylurea receptor blockade with glibenclamide reduced cerebral edema and infarct volume. We postulated that glibenclamide administered during the early stages of stroke might foster neuroprotective microglial activity through ATP-sensitive potassium (KATP) channel blockade. We found in vitro that BV2 cell line showed upregulated expression of KATP channel subunits in response to pro-inflammatory signals and that glibenclamide increases the reactive morphology of microglia, phagocytic capacity and TNFα release. Moreover, glibenclamide administered to rats 6, 12 and 24h after transient Middle Cerebral Artery occlusion improved neurological outcome and preserved neurons in the lesioned core three days after reperfusion. Immunohistochemistry with specific markers to neuron, astroglia, microglia and lymphocytes showed that resident amoeboid microglia are the main cell population in that necrotic zone. These reactive microglial cells express SUR1, SUR2B and Kir6.2 proteins that assemble in functional KATP channels. These findings provide that evidence for the key role of KATP channels in the control of microglial reactivity are consistent with a microglial effect of glibenclamide into the ischemic brain and suggest a neuroprotective role of microglia in the early stages of stroke. [Copyright &y& Elsevier]

Abstract: Recent genome-level innovations have enabled the identification of the entire cadre of genes that are expressed in specific tissues at particular developmental times. However, to be informative as to how individual cell types develop, this process relies upon the successful and efficient purification of cells for a particular tissue. Here, we describe a method to isolate cardiac cells from Drosophila embryos. We generated transgenic embryos in which a cardiac-specific enhancer of the Sulphonylurea receptor (Sur) gene drove expression of the green fluorescent protein (GFP) gene. Homogenized embryos were subjected to fluorescence activated cell sorting (FACS), resulting in approximately 50,000 cardiac cells purified. The prevalence of cardiac cells in the purified population was high, based upon a significant enrichment for cardiac-specific marker genes, including Sur and Toll. This enrichment also enabled the identification of cardiac-specific alternatively spliced isoforms of the Zasp66 gene. In the future, this approach can be used to describe the cardiac transcriptome of Drosophila at distinct stages of embryonic development. [Copyright &y& Elsevier]

The pancreatic β-cell ATP-sensitive K channel (K channel) plays a critical role in glucose homeostasis by linking glucose metabolism to electrical excitability and insulin secretion. Changes in the intracellular ratio of ATP/ADP mediate the metabolic regulation of channel activity. The β-cell K channel is a hetero-octameric complex composed of two types of subunits: four inward-rectifying potassium channel pore-forming (Kir6.2) subunits and four high-affinity sulfonylurea receptor 1 (SUR1) subunits. Kir6.2 and SUR1 are encoded by the genes KCNJ11 and ABCC8, respectively. Mutations in these genes can result in congenital hyperinsulinism and permanent neonatal diabetes. This review highlights the important role of the β-cell K channel in glucose physiology and provides an introduction to some of the other review articles in this special edition of the Reviews in Endocrine and Metabolic Disorders. [ABSTRACT FROM AUTHOR]

ATP-sensitive K+ (KATP) channels in the kidney are considered to play roles in regulating membrane potential according to changes in the intracellular ATP concentration. They are composed of two types of subunits; the pore subunits (Kir6.1, Kir6.2), which are members of the inwardly rectifying K+ channel family, and the regulatory subunits, the sulphonylurea receptors, which belong to the ATP-binding cassette (ABC) superfamily. The sulphonylurea receptors (SURs) are receptors of sulphonylureas widely used for the treatment of type 2 diabetes mellitus. The SURs are divided into two isoforms, SUR1 and SUR2, the latter was further divided into SUR2A and SUR2B. In the present study, we have investigated the mRNA expression by RT-PCR assay, and protein expression profiles by immunoblotting, immunohistochemistry, and immunoelectron microscopy with anti SUR2A and anti SUR2B antibodies. RT-PCR detected the presence of mRNA transcripts of the SUR2A and SUR2B, while SUR1 mRNA was barely detected. In immunoblotting, SUR2A protein was detected distinctly in the microsomal fraction, weakly in the mitochondrial fraction and at negligible level in the cell membrane fraction. In contrast, the SUR2B protein was detected intensely in the microsomal fraction, with a low level in the mitochondrial fraction and scarcely in the cell membrane fraction. In immunohistochemistry SUR2A and SUR2B proteins were widely distributed in renal tubular epithelial cells, glomerular mesangial cells, and the endothelium and the smooth muscle of blood vessels. In immunoelectron microscopy, the immunoreactivity was localized in the endoplasmic reticulum and mitochondria throughout the epithelial cells for SUR2A, and dominantly in the apical cytoplasm of the cells for SUR2B. In conclusion, the regulatory subunits of the KATP channel in the rat kidney are SUR2A and SUR2B; they also are candidate regulatory subunits for the mitochondrial KATP channel. [ABSTRACT FROM AUTHOR]

Abstract: Cardiac development proceeds via the activation of a complex network of regulatory factors which both directly and indirectly impact downstream cardiac structural genes. In Drosophila, the NK homeodomain transcription factor Tinman is critical to cardiac specification and development via the activation of a number of key regulatory genes which mediate heart development. In this manuscript, we demonstrate that Tinman also functions in Drosophila to directly activate transcription of the ATP binding cassette gene Sulphonylurea receptor (Sur). Cardiac expression of Sur is regulated by Tinman via an intron enhancer which first becomes active at stage 12 of embryogenesis, and whose function is restricted to the Tin cardial cells by the end of embryogenesis. Cardiac Sur enhancer activity subsequently persists through larval and adult development, but interestingly becomes modulated in several unique subsets of Tin-expressing cardial cells. The cardiac enhancer contains four binding sites for Tinman protein; mutation of two of these sites significantly reduces enhancer activity at all stages of development, and activation of the wild-type enhancer by ectopic Tinman protein confirms Sur is a direct target of Tinman transcriptional activation. These findings delineate at the molecular level specific sub-types of Tin cardial cells, and define an important regulatory pathway between two Drosophila genes for which mutations in human homologs have been shown to result in cardiac disease. [Copyright &y& Elsevier]

Background and purpose:ATP-sensitive K+ (KATP) channels are composed of pore-forming subunits (Kir6.x) and of sulphonylurea receptors (SUR). Both sulphonylureas and KATP channel openers act by binding to SUR. Sulphonylureas reach their binding site from the cytosol but it remains unknown whether this holds for openers too.Experimental approach:A poorly membrane-permeant sulphonic acid derivative of the benzopyran-type opener, bimakalim, was synthesized, descyano-bimakalim-6-sulphonic acid (BMSA). Binding of BMSA and bimakalim was compared in membranes and intact cells expressing the Kir6.2/SUR2B channel and channel opening was compared in inside-out patches and whole cells.Key results:In membranes, bimakalim and BMSA bound to Kir6.2/SUR2B with Ki values of 61 nM and 4.3 μM, showing that the negative charge decreased affinity 69-fold. In intact cells, however, binding of BMSA was much weaker than in membranes (75-fold) whereas that of bimakalim was unchanged. The Ki value of BMSA decreased with increasing incubation time. In inside-out patches, bimakalim (1 μM) and BMSA (100 μM) opened the Kir6.2/SUR2B channel closed by MgATP to a similar degree whereas in whole-cell experiments, only bimakalim was effective.Conclusions and implications:Despite its negative charge, BMSA is an effective channel opener. The fact that BMSA binds and acts more effectively when applied to the inner side of the cell membrane shows that benzopyran openers reach their binding site at SUR from the cytosol. This suggests that the binding pocket of SUR is only open on the cytoplasmic side.British Journal of Pharmacology (2006) 149, 199–205. doi:10.1038/sj.bjp.0706858; published online 14 August 2006 [ABSTRACT FROM AUTHOR]

ATP-sensitive potassium (KATP) channels conduct potassium ions across cell membranes and thereby couple cellular energy metabolism to membrane electrical activity. Here, we report the heterologous expression and purification of a functionally active KATP channel complex composed of pore-forming Kir6.2 and regulatory SUR1 subunits, and determination of its structure at 18 Å resolution by single-particle electron microscopy. The purified channel shows ATP-ase activity similar to that of ATP-binding cassette proteins related to SUR1, and supports Rb+ fluxes when reconstituted into liposomes. It has a compact structure, with four SUR1 subunits embracing a central Kir6.2 tetramer in both transmembrane and cytosolic domains. A cleft between adjacent SUR1s provides a route by which ATP may access its binding site on Kir6.2. The nucleotide-binding domains of adjacent SUR1 appear to interact, and form a large docking platform for cytosolic proteins. The structure, in combination with molecular modelling, suggests how SUR1 interacts with Kir6.2. [ABSTRACT FROM AUTHOR]

Abstract: Protopine is an isoquinoline alkaloid purified from Corydalis tubers and other families of medicinal plants. The purpose of the present study was to investigate the effects of protopine on KATP channels and big conductance (BKCa) channels. Protopine concentration-dependently inhibited KATP channel currents in human embryonic kidney cells (HEK-293) which were cotransfected with Kir6.1 and sulfonylurea receptor 1 (SUR1) subunits, but not that with Kir6.1 cDNA transfection alone. At 25 μM, protopine reversibly decreased Kir6.1/SUR1 currents densities from −17.4±3 to −13.2±2.4 pA/pF at −60 mV (n=5, P&#60;0.05). The heterologously expressed mSlo-encoded BKCa channel currents in HEK-293 cells were not affected by protopine (25 μM), although iberiotoxin (100 nM) significantly inhibited the expressed BKCa currents (n=5, P&#60;0.05). In summary, protopine selectively inhibited KATP channels by targeting on SUR1 subunit. This discovery may help design specific agents to selectively modulate the function of Kir6.1/SUR1 channel complex and facilitate the understanding of the structure–function relationship of specific subtype of KATP channels. [Copyright &y& Elsevier]

The ATP-sensitive K+ channel (KATP) is a complex composed of an inwardly rectifying, pore-forming subunit (Kir 6.1 and Kir 6.2) and the sulfonylurea receptor (SUR1 and SUR2). In gastrointestinal smooth muscle, these channels are important in regulating cell excitability. We examined the molecular composition of the KATP channel in mouse colonic smooth muscle and determined its activity in the pathophysiological setting of experimental colitis. Following 7 days of dextran sulfate sodium (DSS) treatment in drinking water, colonic inflammation was scored by histology and physical signs. In whole cell recordings, levcromakalim-induced currents were significantly larger in inflamed cells. In cell-attached patch recordings of single channel events, levcromakalim enhanced the bursting duration in inflamed cells. The single-channel conductance of ∼42 pS was not altered with inflammation, mRNA for both Kir 6.1 and 6.2 were detected by RT-PCR. Kir 6.1 was localized to the plasma membrane, whereas Kir 6.2 was mainly detected in the cytosol by immunohistochemistry. Quantitative PCR showed that Kir 6.1 gene expression was upregulated by almost 22-fold, whereas SUR2B was downregulated by threefold after inflammation. Thus decreased motility of the colon during inflammation may be associated with changes in the transcriptional regulation of Kir 6.1 and SUR2B gene expression. [ABSTRACT FROM AUTHOR]

Hyperinsulinism in infancy (HI) is a condition of neonates and early childhood. For many years the pathophysiology of this potentially lethal disorder was unknown. Advances in the genetics, histopathology and molecular physiology of this disease have now provided insights into the causes of β-cell dysfunction and revealed levels of diversity far in excess of our previous knowledge. These include defects in ion channel subunit genes and mutations in several enzymes associated with β-cell metabolism and anaplerosis. In most cases, β-cell pathophysiology leads to an alteration in the function of ATP-sensitive K+ channels. This can manifest as ‘channelopathies’ of KATP channels through gene defects in ABCC8 and KCNJ11 (Ch.11p15); or as a result of ‘metabolopathies’ through defects in the genes encoding glucokinase (GCK, Ch.7p15–p13), glutamate dehydrogenase (GLUD1, Ch.10q23.3) and short-chain L-3-hydroxyacyl-CoA dehydrogenase (HADHSC, Ch.4q22–q26). This review focuses upon the relationship between the causes of HI and therapeutic options. Copyright © 2004 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

1 In this study, we have used Kir6.1 Kir6.2 chimcrie proteins and current recordings to investigate the molecular basis of PNU-37883A inhibition of cloned KATP channels. 2 Rat Kir6.1, Kird.2 and K.ir6.1Kir6.2 chimeras were co-expressed with either SUR2B or SURL following RNA injection into Xeftopus oocytes, and fractional inhibition of KATP currents by IOμM PNU-37883A reported. 3 Channels containing Kir6.l SUR2B were more sensitive to inhibition by PNU-37883A than those containing Kir6.2 SUR2B (mean fractional inhibition: 0.70. cf. 0.07). 4 On expression with SUR2B, a chimcrie channel with the Kir6.1 pore and the Kir.6.2 amino- and carboxy-terminal domains was PNLI-37NN3A insensitive (0.06). A chimera with the Rirfil carboxy-terminal and Kir6.2 amino-terminus and pore was inhibited (0.48). These results, and those obtained with other chimeras, suggest that the C-terminus is an important determinant of PNU-37883A inhibition of Kir6.1. Similar results were seen when constructs were co-expressed with SI JRI. Further chemeric constructs localised PNU-37883A sensitivity to an 81 amino-acid residue section in the Kir6.l carboxy-terminus. 5 Our data show that structural differences between Kir6.l and Kir6.2 are important in determining sensitivity to PNU-37883A. Tins compound ma) prove useful in probing the structural and functional differences between the two channel subtypes. [ABSTRACT FROM AUTHOR]

We have investigated the effects of MCC-134 (1-[4-(1H-imidazol-1-yl)benzoyl]-N-methyl-cyclobutanecarbothioamide) on membrane currents and ATP-sensitive K+ channel (KATP channel) opener-induced currents in pig urethra by use of patch-clamp techniques (conventional whole-cell configuration and nystatin perforated patch recordings). Tension measurement was also performed to study the effects of MCC-134 on the resting tone of pig urethral strips. MCC-134 reduced the resting tone of pig urethra in a concentration-dependent manner (EC50=6 μM). The MCC-134 (30 μM)-induced relaxation was suppressed by glibenclamide. In voltage-clamp experiments, MCC-134 produced a concentration-dependent inward K+ current which was suppressed by application of glibenclamide at a holding potential of −50 mV (symmetrical 140 mM K+ conditions). Application of MCC-134 enhanced diazoxide-induced inward currents and inhibited pinacidil-induced inward currents in a concentration-dependent manner at −50 mV. These results suggest that MCC-134 induces glibenclamide-sensitive KATP currents in pig urethra. [Copyright &y& Elsevier]

Aims/hypothesis. We investigated the pharmacological properties of two novel ATP sensitive potassium (KATP) channel openers, 6-Chloro-3-isopropylamino-4H-thieno[3,2-e]-1,2,4-thiadiazine 1,1-dioxide (NNC 55-0118) and 6-chloro-3-(1-methylcyclopropyl)amino-4H-thieno[3,2-e]-1,2,4-thiadiazine 1,1-dioxide (NN414), on the cloned cardiac (Kir6.2/SUR2A), smooth muscle (Kir6.2/SUR2B) and pancreatic beta cell (Kir6.2/SUR1) types of KATP channel. Methods. We studied the effects of these compounds on whole-cell currents through cloned KATP channels expressed in Xenopus oocytes or mammalian cells (HEK293). We also used inside-out macropatches excised from Xenopus oocytes. Results. In HEK 293 cells, NNC 55-0118 and NN414 activated Kir6.2/SUR1 currents with EC50 values of 0.33 µmol/l and 0.45 µmol/l, respectively, compared with that of 31 µmol/l for diazoxide. Neither compound activated Kir6.2/SUR2A or Kir6.2/SUR2B channels expressed in oocytes, nor did they activate Kir6.2 expressed in the absence of SUR. Current activation was dependent on the presence of intracellular MgATP, but was not supported by MgADP. Conclusion/interpretation. Both NNC 55-0118 and NN414 selectively stimulate the pancreatic beta-cell type of KATP channel with a higher potency than diazoxide, by interaction with the SUR1 subunit. The high selectivity and efficacy of the compounds could prove useful for treatment of disease states where inhibition of insulin secretion is beneficial. [ABSTRACT FROM AUTHOR]

The majority of the most severe cases of congenital hyperinsulinism (HI) are caused by defects in the β-cell adenosine triphosphate (ATP)-sensitive potassium channel and usually require pancreatectomy to control blood sugar levels. In contrast to the recent advances in understanding the pathophysiology and genetic bases of HI, the histologic classification of this condition remains controversial. A recent proposal to classify the HI pancreata into diffuse and focal forms has drawn much interest because of its relative simplicity and its good correlation with the genetic abnormalities. We undertook a retrospective study to determine whether this classification scheme could be applied to 38 pancreata resected for HI at our institution. We also obtained leukocyte genomic DNA from 29 cases and screened the exons of ABCC8 and KCNJ11 genes for the presence of mutations. Nineteen cases (50.0%) were histologically classified as diffuse HI and 14 cases (36.8%) were categorized as focal form. The mutational analysis revealed that 14 of the 16 diffuse cases analyzed had either homozygous or compound heterozygous mutations of ABCC8 or KCNJ11 and 7 of 10 focal cases had only the paternally inherited mutations, consistent with the previous observations. Two patients (5.3%) had normal pancreatic histology but had persistent hypoglycemia postoperatively, leaving the possibility of residual focal lesion. Three of 38 cases (7.9%) did not fit well into either diffuse or focal category. Two cases differed from the described pattern for the diffuse form in that the nuclear enlargement was confined to a single area of the pancreas. The other case had a focal lesion but β-cell nuclear enlargement was present in nonadjacent areas. Mutations for typical diffuse or focal HI were not identified in two of these three equivocal cases. We conclude from this study that nearly 90% of HI cases can be classified into either a diffuse or a focal form. However, a small percentage of cases represented a diagnostic challenge. [ABSTRACT FROM AUTHOR]

ATP-sensitive K (KATP) channels are the targets for a number of therapeutic drugs, including the sulphonylureas used to treat type 2 diabetes, and KATP channel openers used to treat hypertension and angina. The tissue selectivity of agents that modulate KATP channels is due to the differential expression of sulphonylurea receptor (SUR) subunits (SUR1 in pancreatic β-cells, SUR2A in cardiac and skeletal muscles, and SUR2B in smooth muscle). Simple sulphonylureas such as tolbutamide and gliclazide block channels containing SUR1, but not those containing SUR2, with high affinity. Glibenclamide, glimepiride and repaglinide, by contrast, inhibit both SUR1- and SUR2-containing channels. Differences in drug selectivity and reversibility have provided insight into the nature of the drug binding pocket on the sulphonylurea receptor subunits. This will be the basis for the development of more tissue-specific drugs, reducing the risk of unwanted side-effects. [Copyright &y& Elsevier]

Hypoglycaemic agents such as sulphonylureas and the newer group of "glinides" stimulate insulin secretion by closing ATP-sensitive potassium (KATP) channels in pancreatic beta cells, but have varying cross-reactivity with related channels in extrapancreatic tissues such as heart, vascular smooth and skeletal muscle. Experiments on the structure-function relationships of recombinant KATP channels and the phenotypes of mice deficient in different KATP channel subunits have provided important insights into the mechanisms underlying sulphonylurea selectivity, and the potential consequences of KATP channel blockade outside the pancreatic beta cell. The different pharmacological properties of KATP channels from beta cells compared with those from cardiac, smooth and skeletal muscle, are accounted for by the expression of alternative types of sulphonylurea receptor, with non-identical drug binding sites. The sulphonylureas and glinides are found to fall into two groups: one exhibiting selectivity for beta cell sulphonylurea receptors (SUR1), and the other blocking cardiovascular and skeletal muscle sulphonylurea receptors (SUR2) with potencies similar to their action on SUR1. In seeking potential side effects of KATP channel inhibitors in humans, it is essential to take these drug differences into account, along with the probability (suggested by the studies on KATP channel knockout mice) that the effects of extrapancreatic KATP channel inhibition might be either subtle or rare. Further studies are still required before a final decision can be made on whether non-selective agents are appropriate for the therapy of Type 2 diabetes. [ABSTRACT FROM AUTHOR]

Aims/hypothesis. ATP-sensitive potassium (KATP) channels are crucial for the regulation of insulin secretion from pancreatic beta cells and mutations in either the Kir6.2 or SUR1 subunit of this channel can cause congenital hyperinsulinism (CHI). The aim of this study was to analyse the functional consequences of four CHI mutations (A1457T, V1550D and L1551V in SUR1, and K67N in Kir6.2) recently identified in the Finnish population. Methods. Wild type or mutant Kir6.2 and SUR1 subunits were coexpressed in Xenopus oocytes. The functional properties of the channels were examined by measuring currents in intact oocytes or giant inside-out membrane patches. Surface expression was measured by enzyme-linked immunosorbance assay, using HA-epitope-tagged subunits. Results. Two mutations (A1457T and V1550D) prevented trafficking of the channel to the plasma membrane. The L1551V mutation reduced surface expression 40-fold, and caused loss of MgADP and diazoxide activation. Both these factors will contribute to the lack of KATP current activation observed in response to metabolic inhibition in intact oocytes. The L1551V mutation also increased the channel open probability, thereby producing a reduction in ATP-sensitivity (from 10 µmol/l to 120 µmol/l). The fourth mutation (K67N mutation in Kir6.2) did not affect surface expression nor alter the properties of KATP channels in excised patches, but resulted in a reduced KATP current amplitude in intact cells on metabolic inhibition, through an unidentified mechanism. Conclusion/interpretation. The four CHI mutations disrupted KATP channel activity by different mechanisms. Our results are discussed in relation to the CHI phenotype observed in patients with these mutations. [ABSTRACT FROM AUTHOR]

ATP-sensitive K+ (KATP) channels couple metabolic changes to membrane excitability in vascular smooth muscle cells (SMCs). While the electrophysiological properties of KATP channels have been examined, little is known about the molecular basis of KATP complex in vascular SMCs. We identified and cloned four KATP subunit genes from rat mesenteric artery, namely rvKir6.1, rvKir6.2, rvKirSUR1, and rvSUR2B. These clones showed over 99.6% amino acid sequence identity with other previously reported isoforms. The mRNA expression patterns of the KATP subunits varied among rat aorta, mesenteric artery, pulmonary artery, tail artery, hepatic artery, and portal vein. Heterologous co-expression of rvKir6.1 and rvSUR2B yielded functional KATP channels that were inhibited by glibenclamide, and opened by pinacidil. Our results for the first time reported the expression of four KATP subunits in same vascular tissues, unmasking the diversity of native KATP channels in vascular SMCs. [Copyright &y& Elsevier]

The ATP-sensitive potassium channel is made up of four pore forming Kir6.2 subunits, surrounded by four regulatory sulphonylurea receptor (SUR) subunits. The latter subunit contains two nucleotide-binding folds (NBFs) that confer the ability on the channel to sense changes in the metabolic status ([ATP]/[ADP]) of the cell and couple the changes to the membrane potential of the cell. In an attempt to better understand the mechanisms by which NBFs influence the activity of the channel, we have expressed the NBF domains with C-terminally added epitopes (FLAG to NBF1 and His6 to NBF2) in Escherichia coli and the rabbit reticulocyte lysate system and examined the ability of these domains to interact with each other and with Kir6.2. Both NBFs could be expressed to high levels in E. coli and purified to homogeneity from inclusion bodies. Re-folding of the proteins proved to be unsuccessful. However, we were able to obtain small amounts of radio-labelled NBFs in a soluble state. Using co-immunoprecipitation, we demonstrate that the radio-labelled NBF1 and NBF2 interact with each other. Neither of the NBFs bound to Kir6.2 expressed in the presence of canine microsomes. [Copyright &y& Elsevier]

Aims/hypothesis. α-Endosulphine, a protein that belongs to the cAMP-regulated-phosphoprotein family, has been reported to modulate insulin secretion in vitro through interaction with the pancreatic beta-cell ATP-sensitive potassium (KATP) channel. In this study, we analysed the tissue distribution of α-endosulphine and determined its pancreatic cellular localization. Methods. Quantitative tissue distribution of α-endosulphine was studied by RIA on tissue extracts and cellular/subcellular localization was done using immunocytochemistry, morphometry and western blot analysis. α-Endosulphine and somatostatin release from RINT-3 somatostatin-secreting cells was quantified by RIA. Results. α-Endosulphine, concentrated particularly in the central nervous system, was also detected in a wide variety of tissues including the pancreas. Immunohistochemistry analysis of adult rat pancreatic sections showed that α-endosulphine localized in somatostatin δ cells, where its expression increased during post-natal development. Immunoreactive cells were detected from foetal age E19, and the number of somatostatin cells co-expressing α-endosulphine increased with developmental age from E19 until adult. α-Endosulphine, highly expressed in the cytoplasm of RINT3 somatostatin-secreting cell line, was recovered in the particulate fraction of RINT3 cell extracts but was not co-secreted with somatostatin. Conclusion/interpretation. α-Endosulphine is expressed in all tissues tested including pancreas and is also detected in plasma. Pancreatic α-endosulphine is specifically localized in somatostatin δ cells. This cytosolic protein is not co-secreted with somatostatin and could be physically associated with particulate components of the cells. These findings are not in favour of an endocrine/paracrine effect of α-endosulphine on the beta-cell KATP channel. [ABSTRACT FROM AUTHOR]

1 α-Endosulphine, isolated as an endogenous equivalent for sulphonylureas, is a 121,amino acids protein of 19 kDa apparent molecular mass, member of a cyclic AMP-regulated phosphoprotein family- We have previously shown that α-endosulphine inhibits sulphonylurea binding and K[sub ATP] channel activity, thereby stimulating basal insulin secretion. 2 We now describe that in the perfused rat pancreas, no stimulation was detected and that α endosulphine inhibited glucose stimulated insulin release, This inhibition was dose-dependent and affected both phases of insulin secretion. 3 This inhibitory effect of α-endosulphine also occurred on MIN6 β-cells when insulin release was stimulated either by glucose, sulphonylureas or a high K depolarization. Inhibition was concentration -dependent with a half-maximal inhibition at 0.5 μM and was mirrored by inhibition of calcium influx. 4 Electrophysiological experiments demonstrated, in comparison to the effects of the sulphonylurea tolbulamide, that these inhibitory effects were linked to a direct inhibition of L-type Ca[sup2+]-channels and were independent from a regulation of K[sub ATP] channels. 5 Although α-endosulphine is able to stimulate insulin release under specific conditions acting via modulation of A[subATP] channel activity, the present study suggests that, under physiological conditions, the peptide mainly acts to block voltage-gated Ca2 -channels This block leads to the inhibition of calcium influx and triggers inhibition of insulin release. 6 We conclude that α-endosulphine is not -exclusively an endogenous equivalent for sulphonylureas and not solely a K[sub ATP]. channel regulator. [ABSTRACT FROM AUTHOR]

Aims/hypothesis: Sulphonylureas stimulate insulin secretion by closing ATP-sensitive potassium (KATP) channels in the pancreatic beta-cell membrane. KATP channels are also found in other tissues, including heart and smooth muscle, where they link cellular metabolism to electrical activity. The sulphonylurea gliclazide blocks recombinant beta-cell KATP channels (Kir6.2/SUR1) but not heart (Kir6.2/SUR2A) or smooth muscle (Kir6.2/SUR2B) KATP channels with high potency. In this study, we examined the specificity of gliclazide for the native (as opposed to recombinant) KATP channels in beta cells, heart and smooth muscle. Methods: The action of the drug was studied by whole-cell current recordings of native KATP channels in isolated pancreatic beta-cells and myocytes from heart and smooth muscle. Results: Gliclazide blocked whole-cell beta-cell KATP currents with an IC50 of 184 ± 30 nmol/l (n = 6–10) but was much less effective in cardiac and smooth muscle (IC50s of 19.5 ± 5.4 μmol/l (n = 6–12) and 37.9 ± 1.0 μmol/l (n = 5–10), respectively). In all three tissues, the action of the drug on whole-cell KATP currents was rapidly reversible. In inside-out patches on beta-cells, gliclazide (1 μmol/l) produced a maximum of 66 ± 13 % inhibition (n = 5), compared with more than 98 % block in the whole-cell configuration. Conclusion/interpretation: Gliclazide is a high-potency sulphonylurea which shows specificity for the pancreatic beta-cell KATP channel over heart and smooth muscle. In this respect, it differs from glibenclamide. The difference in the maximal block observed in the excised patch and whole-cell recordings from beta-cells, may be due to the absence of intracellular Mg-nucleotides in the excised patch experiments. [Diabetologia (2001) 44: 1019–1025] [ABSTRACT FROM AUTHOR]

Aims/hypothesis. The carbamoylbenzoic acid derivative repaglinide is a potent short-acting insulin secretagogue that acts by closing ATP-sensitive potassium (KATP) channels in the plasma membrane of the pancreatic beta cell. In this paper we investigated the specificity of repaglinide for three types of cloned (KATP) channel composed of the inwardly rectifying potassium channel Kir6.2 and either the sulphonylurea receptor SUR1, SUR2A or SUR2B, corresponding to the beta cell, cardiac and either smooth muscle types of KATP channel, respectively. Methods. The action of the drug was studied by whole-cell current recordings of KATP channels expressed either in Xenopus oocytes or mammalian cells (HEK293). We also used inside-out macropatches excised from Xenopus oocytes for detailed analysis of repaglinide action. Results. The drug blocked all three types of KATP channel with similar potency, by interacting with a low-affinity site on the pore-forming subunit of the channel (Kir6.2: half-maximal inhibition 230 μmol/l) and with a high-affinity site on the regulatory subunit, the sulphonylurea receptor (SUR: half-maximal inhibition 2–8 nmol/l). There was no difference in potency between channels containing SUR1, SUR2A or SUR2B. MgADP potentiated the inhibitory effect of repaglinide on Kir6.2/SUR1 and (to a lesser extent) Kir6.2/SUR2B, but not on Kir6.2/SUR2A. Conclusion/interpretation. Repaglinide interacts with a site common to all three types of sulphonylurea receptor leading to inhibition of the KATP channel. The fact that MgADP potentiated this effect in the case of the beta cell, but not cardiac, type of channel could help explain why the drug shows no adverse cardiovascular side-effects in vivo. [Diabetologia (2001) 44: 747–756] [ABSTRACT FROM AUTHOR]

The subunits of the pancreatic ATP-sensitive potassium channel Kir6.2 and the sulphonylurea receptor (SUR1) contain endoplasmic reticulum (ER) retention signals (RKR), which prevent their plasma membrane expression when expressed individually. When co-expressed, however, these signals are masked and the complex traffics to the plasma membrane. To investigate this further, we have expressed epitope-tagged chimaeras between Kir6.2 and Kir2.1 (which traffics to the membrane independently of SUR1) in Xenopus oocytes alone and together with SUR1. By staining sections of the oocytes, we show that, in addition to the ER retention signal present in the distal C-terminus, the M2 transmembrane and the proximal C-terminal regions also contribute to the inability of Kir6.2 to traffic to the membrane in the absence of SUR1. Furthermore, by staining the whole oocytes for the hexa-histidine tag attached to the N-terminus of SUR1, we provide direct experimental evidence that the N-terminus of SUR1 is extracellular. [ABSTRACT FROM AUTHOR]

Aims/hypothesis. The sulphonylurea receptor is a subunit of the ATP-sensitive potassium channel in the pancreatic beta cell. Mutations at nt –3 of the splice acceptor site of exon 16 and a silent mutation in exon 18 of the gene for the sulphonylurea receptor (SUR1) associate with Type II (non-insulin-dependent) diabetes mellitus in several independent populations. We investigated whether these gene variants associate with changes in the pattern of glucose-stimulated insulin secretion.¶Methods. Subjects who had normal glucose tolerance (n = 67) and subjects with an impaired glucose tolerance (n = 94), originating from two independent studies, were included in the study. Beta-cell function and insulin sensitivity were assessed by the hyperglycaemic clamp.¶Results. Frequencies of the exon 16 –3t allele in the normal and impaired glucose tolerant groups were 46 % and 44 % respectively (p = NS). The more rare exon 18 T allele showed frequencies of 5 and 7 % respectively (p = NS). We observed an approximately 25 % reduced second-phase insulin secretion in carriers of the exon 16 –3t allele in both groups (p < 0.05). Estimates of insulin sensitivity did not show differences between carriers and non-carriers. The variant in exon 18 and the combined presence of variants in exon 16 and exon 18 were not associated with differences in insulin secretion or insulin sensitivity in our study groups.¶Conclusion/interpretation. The diabetes associated exon 16 –3t variant of the SUR1 gene associates with a functional change of the beta cell as reflected by reduced second-phase insulin secretion in response to a standardized hyperglycaemia in normal and impaired glucose tolerant subjects. [Diabetologia (2000) 43: 515–519] [ABSTRACT FROM AUTHOR]

Aims/hypothesis. We have analysed to what extent two previously reported single nucleotide polymorphisms in the sulphonylurea receptor gene ( SUR1) are associated with Type II (non-insulin-dependent) diabetes mellitus in The Netherlands. Furthermore, we estimated haplotype frequencies in control and diabetic populations, including data extracted from three other studies. Methods. Subjects with Type II diabetes ( n = 388) and normoglycaemic subjects (n = 336) were randomly selected from two population-based studies, the Hoorn and Rotterdam studies. DNA was typed for variants in exon 16 (-3 c→ t variant in the splice acceptor site) and exon 18 (Thr759Thr, AC C→AC T). Results. The genotype frequencies in both populations were similar. We observed an association of the exon 16–3 t variant with Type II diabetes (allele frequencies 0.41 % vs 0.48 % in NGT and Type II diabetes, respectively, p = 0.01). There was no association between Type II diabetes and the variant in exon 18 or the combination of both variants ( p > 0.5). A strong linkage disequilibrium between the exon 16 and exon 18 variants was observed in the diabetic groups but not, or less pronounced, in the control groups from the different studies. Haplotype estimation shows that several different risk haplotypes exist in different Caucasian populations. Conclusion/interpretation. The exon 16–3 t allele of the SUR1 gene is associated with Type II diabetes in the Netherlands. Based on estimated haplotype frequencies in different Caucasian populations we conclude that multiple haplotypes on the SUR1 gene seem to confer a risk for developing Type II diabetes in Caucasians. [Diabetologia (1999) 42: 617–620] [ABSTRACT FROM AUTHOR]

The sulphonylurea receptor (SUR) is the site of action for sulphonylurea derivatives such as glibenclamide, which are widely used as oral hypoglycaemic agents. Sulphonylureas have also been shown to affect urine flow and salt excretion by the kidney; therefore, the use of these drugs may have important implications for the pharmacological manipulation of renal salt handling. The purpose of the present investigation was to increase our understanding of the possible role of SUR in the regulation of renal function by determining the distribution of SUR isoforms within mouse kidney. Immunostaining with anti-SUR antisera revealed specific staining of SUR2B in distal nephron segments of mouse kidney. A diffuse, low level staining was observed in proximal tubules in the inner cortical region. No evidence was found for the presence of SUR2B in intra-renal blood vessels. Reverse-transcription polymerase chain reaction and Western blotting experiments indicated that SUR2B is the only known isoform expressed. These data demonstrate that SUR2B in mouse kidney is expressed in tubule regions that are critical in determining renal salt excretion. [ABSTRACT FROM AUTHOR]

In order to elucidate the direct effects of (±)-5-[4-(6-hydroxy-2, 5, 7, 8-tetramethylchroman-2-yl-methoxy) benzyl]-2,4-thiazolidinedione (Troglitazone), a newly-developed oral hypoglycaemic agent, on pancreatic beta-cell function, in vitro investigation of isolated rat pancreatic islets and a hamster beta-cell line (HIT cell) were performed. Troglitazone stimulates both glucose, and glibenclamide-induced insulin release at a concentration of 10 mol/l in these cells but, conversely, inhibits insulin secretion at 10 mol/l. Glucose uptake in HIT cells is similarly enhanced by 10 mol/l Troglitazone, but is reduced in the presence of 10 mol/l Troglitazone. However, a quantitative immunoblot analysis with a specific antibody for GLUT 2 glucose transporter revealed no significant change in GLUT 2 protein in HIT cells with 10 mol/l Troglitazone. Specific binding of [H]-glibenclamide to beta-cell membranes is replaced by Troglitazone in a non-competitive manner, but 10 mol/l Troglitazone failed to eliminate ATP-sensitive K++ channel activity. These results suggest that Troglitazone has a putative non-competitive binding site at, or in the vicinity of, the sulphonylurea receptor in rat pancreatic islets and HIT cells and that the dual effect of Troglitazone on insulin secretory capacity is mediated through the modulation of glucose transport activity, possibly due to the modification of intrinsic activity in glucose transporter in pancreatic beta cells by this novel agent. [Diabetologia (1995) 38: 24-30] [ABSTRACT FROM AUTHOR]

The central role of reversible protein phosphorylation in regulation of beta-cell function is reviewed and the properties of the protein kinases so far defined in beta cells are summarised. The key effect of Ca to initiate insulin secretion involves activation of a Ca/calmodulin-dependent protein kinase. Potentiation of secretion by agents activating protein kinase A or C appears to involve an increase in the sensitivity of the secretory system to intracellular Ca. The effects of MgATP on the binding of [H]-glibenclamide to the beta-cell sulphonylurea receptor suggest that the properties of this receptor, which controls the activity of ATP-sensitive K-channels, are modulated by phosphorylation. The identity of the kinases and phosphatases responsible is not known but the presence in beta-cell membranes of various kinases not dependent on Ca or cyclic AMP, and including tyrosine kinase, is documented, together with the presence of both Ca-dependent and Ca-independent protein phosphatases. Protein phosphorylation is also involved in regulation of beta-cell Ca fluxes and evidence is presented that protein kinase C activation inhibits Ca signalling by reducing influx of Ca into the beta cell. The identity of the Ca/calmodulin-dependent protein kinase activity in beta cells is discussed. Comparison of its properties towards substrates and inhibitors with those of brain Ca/calmodulin-dependent protein kinase II suggests that the beta-cell enzyme may be similar or identical to the brain enzyme. Evidence from Northern and Western blotting experiments supports this conclusion. These findings are incorporated in a model for control of insulin secretion. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the relationship between expression of sulphonylurea receptors (SUR) and metabolic rate (MR). SUR on monocytes and cells from muscle tissue were detected using fluorescent glibenclamide and flow cytometry. Transmembrane potential differences were detected by oxonol dye fluorescence measurements. A bovine model was used to induce differences in the MR by exposure to different ambient temperatures (4°C and 18°C), by different feeding levels (1.0- and 1.6-fold the metabolizable energy requirement for maintenance) and by α2-adrenergic stimulation. We found that cells from skeletal muscle (m. semimembranosus), immunochemically identified as smooth muscle cells, skeletal muscle fibres and monocytes, responded in comparable fashions to glibenclamide and ATP, i.e. with a depolarization, and to cromakalim with a polarization, suggesting that monocytes are useful indicators of regulatory events occurring in muscle cells. Glibenclamide fluorescence was assumed to represent SUR associated with KATP channels. Significant differences were detected in the percentage of depolarized monocytes in the different variants of the model. A linear correlation between monocytes that bound fluorescent glibenclamide and the MR was evident (with a coefficient of determination of 0.94) and was reproducible following reduction of the MR, by α2-adrenergic stimulation, suggesting that expression is involved in the regulation of whole-body energy expenditure. [ABSTRACT FROM AUTHOR]

The article discusses why ATP-sensitive potassium (KATP) channels areunique among all K+ channels and provides incisive insights into how these critical and opposite electrical switching events occur by studying the biophysical and molecular basis of the differential MgADP regulation of KATP channels of the heart and pancreas. The article presents an insight into functional and structural basis of coupling between MgADP and ATP in molecular machines.

The high affinity receptor for sulphonylureas, expressed on the beta cells of the pancreas, plays a crucial role in the control of insulin secretion. Mutations in the cytoplasmic domain of the sulphonylurea receptor ( SUR) gene that disrupt the regulation of insulin secretion have been previously described. In the present study, the potential role of genetic variation in the SUR gene has been investigated in non-insulin-dependent diabetes mellitus (NIDDM) through linkage studies with microsatellite markers tightly linked to the SUR gene. The microsatellite markers were typed in 346 Mexican-American NIDDM affected sib pairs derived from 176 families and an additional 110 ethnically and geographically matched control subjects. No evidence of linkage, based on allele sharing, or association based on allele frequencies in patients and control subjects, for any microsatellite marker and NIDDM was observed in this population. These results suggest that genetic variation in the SUR gene does not play a major role in susceptibility to NIDDM in the Mexican-American population. [ABSTRACT FROM AUTHOR]

Persistent hypoglycaemia in infancy is most commonly caused by hyperinsulinism. A case is reported of the somatic loss of the maternal 11p in an insulin secreting focal adenoma in association with a germline SUR-1 mutation on the paternal allele in a baby boy with hyperinsulinism diagnosed at 49 days old. A reduction to homozygosity of an SUR-1 mutation is proposed as a critical part of the cause of focal hyperinsulinism. [ABSTRACT FROM AUTHOR]