Immunoglobulin from Insulin-dependent Diabetic Children Inhibits Glucose-induced Insulin Release

Immunogiobulin was separated from islet cell antibody positive plasma of six children with newly diagnosed insulin-dependent (type I) diabetes mellitus. The dynamics of insulin release in response to glucose and partially purified antibodies were determined in dispersed rat islet cells perifused on small columns of Biogel P-2 beads. After perifusion at 5.5 mmol/L D-glucose in the presence of healthy control immunoglobulin, the rate of insulin release increased in a biphasic manner after stimulation with 30 mmol/L D-glucose. In cells exposed to diabetic immunoglobulin, 30 mmol/L D-glucose had little, if any, effect on insulin release. These results suggest that islet cell antibodies in insulin-dependent diabetes may interfere with the insulin release mechanisms in the pancreatic B-cells

Expression of major histocompatibility antigens on pancreatic-islet cells

Insulin-dependent diabetes mellitus is often accompanied by manifestations of autoimmunity and is frequently associated with certain HLA haplotypes, predominantly DR3 and DR4. Because the major histocompatibility antigens are important determinants of the immune response in various tissues, we have investigated their expression on the pancreatic islet cells. Human, mouse, or rat islets of Langerhans, as well as lymphocytes or other differentiated cells, were biosynthetically labeled with radioactive amino acids, lysed in detergent, and immunoprecipitated with several antisera specific for major histocompatibility antigenic groups. The immunoprecipitates were analyzed by NaDodSo4/polyacrylamide gel electrophoresis under reducing conditions followed by autoradiography. The major histocompatibility antigens corresponding to the H-2 K,D molecules in mice, the H1-A in rats, and the HLA-A, -B, and -C in humans were precipitated from both islet and lymphocyte lysates and were accompanied by beta 2-microglobulin. Binding of H-2 antibodies to islet cells was also confirmed by a radioligand assay using 125I-labeled protein A and by indirect immunofluorescence. Analyses in the fluorescence-activated cell sorter revealed that greater than 95% of the cells in the beta-cell-rich fraction were fluorescent, providing further evidence that the pancreatic beta cells express the major histocompatibility antigens. Monoclonal antibodies or mouse alloantisera against HLA-DR or Ia antigens did not react with labeled pancreatic islet cell proteins

Glucose-sensing mechanisms in pancreatic β-cells

The appropriate secretion of insulin from pancreatic β-cells is critically important to the maintenance of energy homeostasis. The β-cells must sense and respond suitably to postprandial increases of blood glucose, and perturbation of glucose-sensing in these cells can lead to hypoglycaemia or hyperglycaemias and ultimately diabetes. Here, we review β-cell glucose-sensing with a particular focus on the regulation of cellular excitability and exocytosis. We examine in turn: (i) the generation of metabolic signalling molecules; (ii) the regulation of β-cell membrane potential; and (iii) insulin granule dynamics and exocytosis. We further discuss the role of well known and putative candidate metabolic signals as regulators of insulin secretion

The imidazoline derivative calmidazolium inhibits voltage-gated Ca2+-channels and insulin release but has no effect on the phospholipase C system in insulin producing RINm5F-cells

The present study shows that the calmodulin antagonist calmidazolium inhibited influx of Ca2+ through voltage-gated Ca2+-channels in clonal insulin producing RINm5F-cells. The mechanism of inhibition may involve both Ca2+-calmodulin-dependent protein kinases and direct binding of calmidazolium to the Ca2+-channel. Calmidazolium did not affect uptake of Ca2+ into intracellular Ca2+-pools, inositol 1,4,5-trisphosphate (InsP3) formation or action on intracellular Ca2+-pools. The calmodulin inhibitor also did not affect glucose utilization or oxidation in RINm5F-cells, speaking against an unspecific toxic effect of the compound. KCl-and ATP-stimulated insulin release from RINm5F-cells was attenuated by calmidazolium, whereas basal hormone secretion was unaffected