Mouse islets exhibit glucose-dependent oscillations in electrical activity, intracellular Ca(2+) and insulin secretion. We developed a mathematical model in which a left shift in glucose threshold helps compensate for insulin resistance. To test this experimentally, we exposed isolated mouse islets to varying glucose concentrations overnight and monitored their glucose sensitivity the next day by measuring intracellular Ca(2+), electrical activity, and insulin secretion. Glucose sensitivity of all oscillation modes was increased when overnight glucose was greater than 2.8mM. To determine whether threshold shifts were a direct effect of glucose or involved secreted insulin, the KATP opener diazoxide (Dz) was coapplied with glucose to inhibit insulin secretion. The addition of Dz or the insulin receptor antagonist s961 increased islet glucose sensitivity, whereas the KATP blocker tolbutamide tended to reduce it. This suggests insulin and glucose have opposing actions on the islet glucose threshold. To test the hypothesis that the threshold shifts were due to changes in plasma membrane KATP channels, we measured cell KATP conductance, which was confirmed to be reduced by high glucose pretreatment and further reduced by Dz. Finally, treatment of INS-1 cells with glucose and Dz overnight reduced high affinity sulfonylurea receptor (SUR1) trafficking to the plasma membrane vs glucose alone, consistent with insulin increasing KATP conductance by altering channel number. The results support a role for metabolically regulated KATP channels in the maintenance of glucose homeostasis.

results in enhanced glucose-stimulated insulin secretion (GSIS). These data provide compelling evidence that TALK-1 influences GSIS by limiting excitability, and suggests a novel mechanism for phospholipid-dependent regulation of beta-cell Ca 2þ entry. 2184-Pos Board B321Investigating Viral Channel Forming Protein VPU with Coarse-Graining Molecular Dynamics Simulation Meng-Han Lin, Wolfgang Fischer. Institute of Biophotonics, Taipei, Taiwan. VPU of HIV has been verified as a channel-forming protein by experiment. The self-assembly process and the oligomer state of VPU are not clear. We use coarse-graining molecular dynamics simulation to study the full-length channel-forming protein VPU in lipid bilayer. The full-length of VPU was constructed by linking the cytoplasm and transmembrane domain solved by NMR. We put different number of VPUs 2, 3, 4, 5 or bigger amount 16, 32 in simulation box. Our results show several binding sites and the oligomer state. In those simulations, the four VPUs form a symmetric bundle which is close to the channel structure. The tetramer was seem to form via a dimer. Not only transmembrane domain but also cytoplasm domain was involved in self-assembly.