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Type 1 diabetes is an autoimmune disease of unknown etiology. Our previous work has shown that a factor present in serum from type 1 diabetic patients causes increased Ca2+ channel activity and apoptotic DNA fragmentation in pancreatic beta-cells. Here we examined the effects of type 1 diabetic serum on primary cerebellar granule cells (CGCs). In CGCs, exposure to type 1 diabetic serum did not cause increased apoptosis or changes in Ca2+ channel activity. However, patient serum did cause modulation of Ca2+ signals in a cell type with triangular soma that exhibited low voltage-gated Ca2+ currents. This cell was present primarily in cultures exposed to type 1 diabetic serum. The presence of low voltage-gated Ca2+ currents and long neuronal dendrites indicated that this unique cell was of neuronal origin and not of glial origin. [ABSTRACT FROM AUTHOR]

Imidazoline compounds have been considered for the treatment of type 2 diabetes. We have now investigated the effects of imidazolines on interleukin (IL)-1beta-induced beta-cell apoptosis and the signal transduction pathways involved. Inhibition of Ca2+ influx into beta-cells by D-600, a blocker of voltage-gated L-type Ca2+ channels, suppressed IL-1beta-induced apoptosis. Our data show that calcineurin, Ca2+/calmodulin-dependent serine/threonine protein phosphatase 2B, is responsible for the effect of Ca2+ on beta-cell apoptosis. We also demonstrate that IL-1beta-mediated apoptosis correlates with expression of inducible nitric oxide synthase (iNOS) and the increase in intracellular production of nitric oxide. An inhibitor of cGMP-dependent protein kinase (PKG), KT5823, suppressed IL-1beta-induced apoptosis, suggesting the involvement of a PKG-dependent pathway in the apoptotic process. One of the major findings in this study is that imidazoline compounds RX871024 and efaroxan, suggested as prototypes of a new generation of drugs against type 2 diabetes, can protect against IL-1beta-induced apoptosis in pancreatic beta-cells, possibly by their inhibition of the expression of iNOS, a key element in the IL-1beta-induced apoptotic pathway in pancreatic beta-cells. These data suggest that imidazoline compounds should be explored as a potential therapeutic agent for the treatment of both type 1 and type 2 diabetes. [ABSTRACT FROM AUTHOR]

Apoptosis is a physiological form of cell death that occurs during normal development, and critical mediators of this process include caspases, reactive oxygen species, and Ca2+. Excessive apoptosis of the pancreatic beta-cell has been associated with diabetes. Consequently, apoptosis research has focused on how infiltrating macrophages or cytotoxic T-cells might kill pancreatic beta-cells using cytokines or death receptor triggering. Meanwhile, the intracellular events in the target beta-cell have been largely ignored. Elucidation of such targets might help develop improved treatment strategies for diabetes. This article will outline recent developments in apoptosis research, with emphasis on mechanisms that may be relevant to beta-cell death in type 1 and type 2 diabetes. Several of the models proposed in beta-cell killing converge on Ca2+ signaling, indicating that the pancreatic beta-cell may be an ideal system in which to carefully dissect the role of Ca2+ during apoptosis. [ABSTRACT FROM AUTHOR]

The effects of RX871024, a compound with an imidazoline structure, on cytoplasmic-free Ca2+ concentration ([Ca2+]i) in mouse pancreatic beta-cells were studied. RX871024 modulates [Ca2+]i by at least two mechanisms. One mechanism involves closure of ATP-regulated K+ channels, resulting in membrane depolarization, opening of voltage-gated L-type Ca2+ channels, and a subsequent increase in [Ca2+]i. Another mechanism, reported here for the first time, deals with RX871024-induced mobilization of Ca2+ from nonmitochondrial thapsigargin-sensitive intracellular stores. Reduced glutathione, inhibitors of cytochrome P-450, and monoaminooxidases A and B blocked this Ca2+ mobilization. It is concluded that the mechanism of RX871024-induced Ca2+ mobilization from intracellular stores involves changes in the oxidation/reduction state of the pancreatic beta-cell and may be controlled by cytochrome P-450. [ABSTRACT FROM AUTHOR]

Recently, it has been proposed that leptin, the ob gene product, influences some steps in the insulin-signaling cascade. The purpose of the present study was to determine whether leptin exerts direct effects on glucose transport in insulin target tissues. Epitrochlearis muscles or isolated adipocytes from male SD rats were incubated in the absence or presence of recombinant leptin (3-1,000 ng/ml), and in the absence or presence of submaximal or maximal insulin concentrations. In skeletal muscle, insulin increased 3-O-methylglucose transport (1.88 +/- 0.21, 4.06 +/- 0.59, and 9.35 +/- 1.90 micromol x ml-1 x h-1, for 0, 0.6, and 12.0 nmol/l insulin, respectively). Leptin exposure (300 ng/ml) for 2 h did not alter the basal, submaximal, or maximal response of glucose transport to insulin in skeletal muscle (1.50 +/- 0.14, 4.76 +/- 0.58, and 9.04 +/- 1.09 micromol x ml-1 x h-1 for 0, 0.6, and 12.0 nmol/l insulin, respectively). Insulin increased glucose transport in rat adipocytes (0.194 +/- 0.007, 1.059 +/- 0.029, and 3.367 +/- 0.143 pmol [14C]glucose x 0.5 ml-1 cell suspension x min-1 for 0, 0.8, and 80 nmol/l insulin, respectively); in vitro exposure to leptin (300 ng/ml) did not alter glucose transport (0.220 +/- 0.006, 1.269 +/- 0.046, and 3.221 +/- 0.285 pmol [14C]glucose x 0.5 ml-1 cell suspension x min-1 for 0, 0.8, and 80 nmol/l insulin, respectively). Similar to our findings in the epitrochlearis muscle, leptin had no direct effect on basal or insulin-stimulated glucose uptake in soleus muscle from ob/ob or lean mice or adipocytes from normal mice. In summary, in vitro exposure of skeletal muscle or adipocytes to recombinant leptin did not alter glucose transport in the absence of insulin, nor did it affect the sensitivity or responsiveness of the glucose transport system to insulin. [ABSTRACT FROM AUTHOR]