Glucose principally regulates insulin secretion in mouse islets by controlling the numbers of granule fusion events per cell.

AIMS/HYPOTHESIS: In dispersed single beta cells the response of each cell to glucose is heterogeneous. In contrast, within an islet, cell-to-cell communication leads to glucose inducing a more homogeneous response. For example, increases in NAD(P)H and calcium are relatively uniform across the cells of the islet. These data suggest that secretion of insulin from single beta cells within an islet should also be relatively homogeneous. The aim of this study was to test this hypothesis by determining the glucose dependence of single-cell insulin responses within an islet. METHODS: Two-photon microscopy was used to detect the glucose-induced fusion of single insulin granules within beta cells in intact mouse islets. RESULTS: First, we validated our assay and showed that the measures of insulin secretion from whole islets could be explained by the time course and numbers of granule fusion events observed. Subsequent analysis of the patterns of granule fusion showed that cell recruitment is a significant factor, accounting for a fourfold increase from 3 to 20 mmol/l glucose. However, the major factor is the regulation of the numbers of granule fusion events within each cell, which increase ninefold over the range of 3 to 20 mmol/l glucose. Further analysis showed that two types of granule fusion event occur: 'full fusion' and 'kiss and run'. We show that the relative frequency of each type of fusion is independent of glucose concentration and is therefore not a factor in the control of insulin secretion. CONCLUSIONS/INTERPRETATION: Within an islet, glucose exerts its main effect through increasing the numbers of insulin granule fusion events within a cell.

Development of encoded particle-polymer arrays for the accelerated screening of antifouling layers.

A multiplexed screening methodology for the rapid development of antifouling polymer surfaces is presented. An array of protein resistant polymer layers with high grafting (>100 mg m(-2)) were polymerized on optically encoded particles. Multiplexed analysis showed a 97% reduction in nonspecific protein adsorption for all polymer layers created.

Protein resistance of dextran and dextran-poly(ethylene glycol) copolymer films.

The protein resistance of dextran and dextran-poly(ethylene glycol) (PEG) copolymer films was examined on an organosilica particle-based assay support. Comb-branched dextran-PEG copolymer films were synthesized in a two step process using the organosilica particle as a solid synthetic support. Particles modified with increasing amounts (0.1-1.2 mg m(-2)) of three molecular weights (10,000, 66,900, 400,000 g mol(-1)) of dextran were found to form relatively poor protein-resistant films compared to dextran-PEG copolymers and previously studied PEG films. The efficacy of the antifouling polymer films was found to be dependent on the grafted amount and its composition, with PEG layers being the most efficient, followed by dextran-PEG copolymers, and dextran alone being the least efficient. Immunoglobulin gamma (IgG) adsorption decreased from ∼5 to 0.5 mg m(-2) with increasing amounts of grafted dextran, but bovine serum albumin (BSA) adsorption increased above monolayer coverage (∼2 mg m(-2)) indicating ternary adsorption of the smaller protein within the dextran layer.