Barriers to the use of islet transplantation as a practical treatment for diabetes include the limited number of available donor pancreata. This project was designed to determine whether the size of the islet could influence the success rate of islet transplantations in rats. Islets from adult rats were divided into two groups containing small (diameter Ͻ125 m) or large (diameter Ͼ150 m) islets. An average pancreas yielded three times more small islets than large. Smaller islets were ϳ20% more viable, with large islets containing a scattered pattern of necrotic and apoptotic cells or central core cell death. Small islets in culture consumed twice as much oxygen as large islets when normalized for the same islet equivalents. In static incubation, small islets released three times more insulin under basal conditions than did large islets. During exposure to high glucose conditions, the small islets released four times more insulin than the same islet equivalencies of large islets, and five times more insulin was released by the small islets in response to glucose and depolarization with K ϩ . Most importantly, the small islets were far superior to large islets when transplanted into diabetic animals. When marginal islet equivalencies were used for renal subcapsular transplantation, large islets failed to produce euglycemia in any recipient rats, whereas small islets were successful 80% of the time. The results indicate that small islets are superior to large islets in in vitro testing and for transplantation into the kidney capsule of diabetic rats. islet transplant; insulin secretion; viability THE RISE IN CASES OF DIABETES MELLITUS in the United States has been called an epidemic. It is the third leading cause of death by disease and rivals heart disease and cancer as a major killer of United States citizens. For unexplained reasons the occurrence of type 1 diabetes is increasing worldwide, and the age of onset has decreased by 3-5 yr over the past decade so that many children now develop diabetes before entering school. The result is that more people with diabetes will spend a larger percentage of their life at risk for developing the chronic complications related to type 1 diabetes. Because the risk for development of most of the chronic complications associated with diabetes is related to glycemic control, significant attention is directed toward novel therapies, such as islet transplantation, to improve glycemic control.Islet transplants in humans were first attempted in the 1980s (7, 8). Initial success rates for human islet transplantation were disappointing, with only 5% of patients receiving transplants achieving partial function (19). Amid the failures were isolated success stories of individuals achieving prolonged reversal of their diabetes for a 1-to 2-yr period (19), which encouraged researchers to continue this approach for the treatment of diabetes. In 2000, islet transplantations were performed successfully on seven patients with diabetes by using a suppression regimen that omitted glucocorticoid...

Intact, isolated nuclei and a nuclear membrane (ghost) preparation were used to study regulation of the movement of small molecules across the Xenopus laevis oocyte nuclear membrane. In contrast to models of the nuclear pore complex, which assume passive bidirectional diffusion of molecules less than 70 kilodaltons, diffusion of intermediate-sized molecules was regulated by the nuclear envelope calcium stores. After depletion of nuclear store calcium by inositol 1,4,5-trisphosphate or calcium chelators, fluorescent molecules conjugated to 10-kilodalton dextran were unable to enter the nucleus. Dye exclusion after calcium store depletion was not dependent on the nuclear matrix because it occurred in nuclear ghosts lacking nucleoplasm. Smaller molecules and ions (500-dalton Lucifer yellow and manganese) diffused freely into the core of the nuclear ghosts and intact nuclei even after calcium store depletion. Thus, depletion of the nuclear calcium store blocks diffusion of intermediate-sized molecules.

The nucleus is surrounded by a double membrane separating it from the cytoplasm. The perinuclear space is continuous with endoplasmic reticulum, and the nuclear outer membrane shares many features with the reticular membrane. We now show that inositol 1,4,5-trisphosphate (InsP3) receptors associated with the nucleus release Ca2+ from isolated Xenopus laevis oocyte nuclei. Electrophysiological measurements of the intracellular InsP3 receptor in its native membrane have not been possible on the fine filamentous endoplasmic reticulum. In this paper, we directly measure InsP3-dependent receptor channels in isolated nuclei. The nuclear InsP3 receptor is activated by InsP3 and modulated by Ca2+. The channel is weakly regulated by ATP, is mildly voltage dependent, and has a greater conductance with monovalent cations than with divalent cations.

Chemokines play a key role in the regulation of central nervous system disease. CXCL10 over-expression has been observed in several neurodegenerative diseases, including multiple sclerosis, Alzheimer's disease and HIV-associated dementia. More recent studies by others and us have shown that CXCL10 elicits apoptosis in fetal neurons. The mechanism of CXCL10-mediated neurotoxicity, however, remains unclear. In this study, we provide evidence for the direct role of Ca(2+) dysregulation in CXCL10-mediated apoptosis. We demonstrate that treatment of fetal neuronal cultures with exogenous CXCL10 produced elevations in intracellular Ca(2+) and that this effect was modulated via the binding of CXCL10 to its cognate receptor, CXCR3. We further explored the association of intracellular Ca(2+) elevations with the caspases that are involved in CXC10-induced neuronal apoptosis. Our data showed that increased Ca(2+), which is available for uptake by the mitochondria, is associated with membrane permeabilization and cytochrome c release from this compartment. The released cytochrome c then activates the initiator active caspase-9. This initiator caspase sequentially activates the effector caspase-3, ultimately leading to apoptosis. This study identifies the temporal signaling cascade involved in CXCL10-mediated neuronal apoptosis and provides putative targets for pharmaceutical intervention of neurological disorders associated with CXCL10 up-regulation.

The nuclear pore complex (NPC) is essential for the transit of molecules between the cytoplasm and nucleoplasm of a cell and until recently was thought to allow intermediate-sized molecules (relative molecular mass of approximately 10,000) to diffuse freely across the nuclear envelope. However, the depletion of calcium from the nuclear envelope of Xenopus laevis oocytes was shown to regulate the passage of intermediate-sized molecules. Two distinct conformational states of the NPC were observed by field emission scanning electron microscopy and atomic force microscopy. A central plug occluded the NPC channel after nuclear calcium stores had been depleted and free diffusion of intermediate-sized molecules had been blocked. Thus, the NPC conformation appears to gate molecular movement across the nuclear envelope.