Enhanced GLP-1- and sulfonylurea-induced insulin secretion in islets lacking leptin signaling.

We have previously reported that the absence of leptin signaling in β-cells enhances glucose-stimulated insulin secretion and improves glucose tolerance in vivo. To investigate the relevance of β-cell leptin signaling in the context of postprandial or therapeutic insulin secretion, we examined the cross talk between leptin and glucagon-like peptide (GLP)-1 and sulfonylurea actions. Single and size-matched islets isolated from control or pancreas-specific leptin receptor knockout (pancreas-ObR-KO) mice were treated either with GLP-1 or with glibenclamide.

Dynamic monitoring of glucagon secretion from living cells on a microfluidic chip.

A rapid microfluidic based capillary electrophoresis immunoassay (CEIA) was developed for on-line monitoring of glucagon secretion from pancreatic islets of Langerhans. In the device, a cell chamber containing living islets was perfused with buffers containing either high or low glucose concentration. Perfusate was continuously sampled by electroosmosis through a separate channel on the chip.

Glucose metabolism, islet architecture, and genetic homogeneity in imprinting of [Ca2+](i) and insulin rhythms in mouse islets.

We reported previously that islets isolated from individual, outbred Swiss-Webster mice displayed oscillations in intracellular calcium ([Ca2+](i)) that varied little between islets of a single mouse but considerably between mice, a phenomenon we termed "islet imprinting." We have now confirmed and extended these findings in several respects. First, imprinting occurs in both inbred (C57BL/6J) as well as outbred mouse strains (Swiss-Webster; CD1).

Continuous operation of microfabricated electrophoresis devices for 24 hours and application to chemical monitoring of living cells.

Microchip electrophoresis is an emerging analytical technology with several useful attributes including rapid separation time, small sample requirements, and automation. In numerous potential applications, such as chemical monitoring or high-throughput screening, it may be desirable to use a system for many analyses without operator intervention; however, long-term operation of microchip electrophoresis systems has received little attention. We have developed a microchip electrophoresis system that can automatically inject samples at 6 s intervals for 24 h resulting in collection of 14,400 assays in one session.

Quantitative monitoring of insulin secretion from single islets of Langerhans in parallel on a microfluidic chip.

Quantification of insulin release from pancreatic islets of Langerhans is of interest for diabetes research. Typical insulin secretion experiments are performed using offline techniques that are expensive, slow, have low-throughput, and require multiple islets. We have developed a microfluidic device for high-throughput, automated, and online monitoring of insulin secretion from individual islets in parallel.

A single mutation in the nonamyloidogenic region of islet amyloid polypeptide greatly reduces toxicity.

Islet amyloid polypeptide (IAPP or amylin) is a 37-residue peptide secreted with insulin by beta-cells in the islets of Langerhans. The aggregation of the peptide into either amyloid fibers or small soluble oligomers has been implicated in the death of beta-cells during type 2 diabetes through disruption of the cellular membrane. The actual form of the peptide responsible for beta-cell death has been a subject of controversy.

Capillary LC-MS for high sensitivity metabolomic analysis of single islets of Langerhans.

Reversed-phase, packed capillary liquid chromatography interfaced by electrospray ionization to mass spectrometry was explored as an analytical method for determination of metabolites in microscale tissue samples using single islets of Langerhans as a model system. With the use of a 75 microm inner diameter column coupled to a quadrupole ion trap mass spectrometer in full scan mode, detection limits of 0.1-33 fmol were achieved for glycoloytic and tricarboxylic acid cycle metabolites.

Effect of decreasing column inner diameter and use of off-line two-dimensional chromatography on metabolite detection in complex mixtures.

Capillary liquid chromatography coupled with electrospray ionization to a quadrupole ion trap mass spectrometer was explored as a method for the analysis of polar anionic compounds in complex metabolome mixtures. A ternary mobile phase gradient, consisting of aqueous acidic, aqueous neutral and organic phases in combination with an aqueous compatible reversed-phase stationary phase allowed metabolites with a wide range of polarities to be resolved and detected. Detection limits in the full scan mode for glycolysis and tricarboxylic acid cycle intermediates were from 0.

Solid-phase extraction sorbent consisting of alkyltrimethylammonium surfactants immobilized onto strong cation-exchange polystyrene resin.

Presented is a solid-phase extraction sorbent material composed of cationic alkyltrimethylammonium surfactants attached to a strong cation-exchange resin via ion-exchange. The original hydrophilic cation-exchange resin is made hydrophobic by covering the surface with alkyl chains from the hydrophobic portion of the surfactant. The sorbent material now has a better ability to extract hydrophobic molecules from aqueous samples.