The ATP-sensitive potassium channel is a key molecular complex for glucose-stimulated insulin secretion in pancreatic ␤ cells. In humans, mutations in either of the two subunits for this channel, the sulfonylurea type 1 receptor (Sur1) or Kir6.2, cause persistent hyperinsulinemic hypoglycemia of infancy. We have generated and characterized Sur1 null mice. Interestingly, these animals remain euglycemic for a large portion of their life despite constant depolarization of membrane, elevated cytoplasmic free Ca 2؉ concentrations, and intact sensitivity of the exocytotic machinery to Ca 2؉ . A comparison of glucose-and meal-stimulated insulin secretion showed that, although Sur1 null mice do not secrete insulin in response to glucose, they secrete nearly normal amounts of insulin in response to feeding. Because Sur1 null mice lack an insulin secretory response to GLP-1, even though their islets exhibit a normal rise in cAMP by GLP-1, we tested their response to cholinergic stimulation. We found that perfused Sur1 null pancreata secreted insulin in response to the cholinergic agonist carbachol in a glucose-dependent manner. Together, these findings suggest that cholinergic stimulation is one of the mechanisms that compensate for the severely impaired response to glucose and GLP-1 brought on by the absence of Sur1, thereby allowing euglycemia to be maintained.Glucose-stimulated insulin secretion by the pancreatic ␤ cell requires the coupling of changes in glucose metabolism to alterations in membrane potential (1-4). In response to a rise in the intracellular ATP/ADP ratio that occurs with glucose metabolism the closure of ATP-sensitive potassium (K ATP ) 1 channels causes the ␤ cell membrane to depolarize. This, in turn, leads to the opening of voltage-gated L-type Ca 2ϩ channels, a rise in the cytoplasmic free Ca 2ϩ concentration ([Ca 2ϩ ] i ), and the subsequent exocytosis of insulin (5). The ␤ cell K ATP channel is an octameric complex of two proteins: an inward-rectifier K ϩ channel, Kir6.2, and the sulfonylurea receptor type 1 (Sur1), which are present in a 4:4 stoichiometry (6, 7). Kir6.2, which forms the channel pore, possesses intrinsic ATP sensitivity (8, 9), whereas Sur1, a member of a superfamily of ATPbinding cassette transporter proteins, provides sites for interaction with Mg-ADP (10). Sulfonylureas, which are widely used for treatment of patients with type 2 diabetes mellitus, act by binding to K ATP channels and stimulating their closure (10).Mutations in Sur1 are a frequent cause of persistent hyperinsulinemic hypoglycemia of infancy (PHHI), an autosomal recessive disorder characterized by excess and unregulated secretion of insulin. Because initial identification of Sur1 as a candidate gene for PHHI by , more than 50 different mutations in this gene, as well as 2 mutations in Kir6.2, have been identified in PHHI patients (12). Analyses of pancreatic ␤ cells from PHHI patients, as well as functional studies of mutated K ATP channels introduced into cultured cells, suggest that impaired K ATP channel...

The contribution of interleukin (IL)-6 signaling in obesity-induced inflammation remains controversial. To specifically define the role of hepatic IL-6 signaling in insulin action and resistance, we have generated mice with hepatocyte-specific IL-6 receptor (IL-6R) alpha deficiency (IL-6Ralpha(L-KO) mice). These animals showed no alterations in body weight and fat content but exhibited a reduction in insulin sensitivity and glucose tolerance. Impaired glucose metabolism originated from attenuated insulin-stimulated glucose transport in skeletal muscle and fat. Surprisingly, hepatic IL-6Ralpha-disruption caused an exaggerated inflammatory response during euglycemic hyperinsulinemic clamp analysis, as revealed by increased expression of IL-6, TNF-alpha, and IL-10, as well as enhanced activation of inflammatory signaling such as phosphorylation of IkappaBalpha. Neutralization of TNF-alpha or ablation of Kupffer cells restored glucose tolerance in IL-6Ralpha(L-KO) mice. Thus, our results reveal an unexpected role for hepatic IL-6 signaling to limit hepatic inflammation and to protect from local and systemic insulin resistance.

Several proteins that are of importance for membrane trafficking in the nerve terminal have recently been characterized. We have used Western blot and immunohistochemistry to show that synaptotagmin, synaptobrevin/VAMP (vesicle-associated membrane protein), SNAP-25 (synaptosomal-associated protein of 25 kDa), and syntaxin proteins are present in cells of the islets of Langerhans in the endocrine pancreas. Synaptotagmin-like immunoreactivity (-LI) was localized to granules within the cytoplasm of a few endocrine cells located in the periphery of the islets, identified as somatostatincontaining cells, and in many nerve fibers within the islets. VAMP-LI was seen in granules of virtually all pancreatic islet cells and also in nerve fibers. SNAP-25-LI and syntaxin-LI were predominantly present in the plasma membrane ofthe endocrine cells, including insulin-producing (I cells. In situ hybridization, using isoform-specific oligonucleotide probes, detected VAMP-2, cellubrevin, SNAP-25, syntaxin 1A, 4, and 5, and munc-18 mRNAs in isolated pancreatic islets and in insulinproducing cells. The results show the presence of several synaptic proteins at protein and mRNA levels in pancreatic islet cells, suggesting that they may have specific roles in the molecular regulation of exocytosis also in insulin-secreting cells.

An oscillatory increase in pancreatic beta cell cytoplasmic free Ca2+ concentration, [Ca2+]i, is a key feature in glucose-induced insulin release. The role of the voltage-gated Ca2+ channel beta3 subunit in the molecular regulation of these [Ca2+]i oscillations has now been clarified by using beta3 subunit-deficient beta cells. beta3 knockout mice showed a more efficient glucose homeostasis compared to wild-type mice due to increased glucose-stimulated insulin secretion. This resulted from an increased glucose-induced [Ca2+]i oscillation frequency in beta cells lacking the beta3 subunit, an effect accounted for by enhanced formation of inositol 1,4,5-trisphosphate (InsP3) and increased Ca2+ mobilization from intracellular stores. Hence, the beta3 subunit negatively modulated InsP3-induced Ca2+ release, which is not paralleled by any effect on the voltage-gated L type Ca2+ channel. Since the increase in insulin release was manifested only at high glucose concentrations, blocking the beta3 subunit in the beta cell may constitute the basis for a novel diabetes therapy.