Excessive secretion of glucagon is a major contributor to the development of diabetic hyperglycemia. Secretion of glucagon is regulated by various nutrients, with glucose being a primary determinant of the rate of alpha cell glucagon secretion. The intra-islet action of insulin is essential to exert the effect of glucose on the alpha cells since, in the absence of insulin, glucose is not able to suppress glucagon release in vivo. However, the precise mechanism by which insulin suppresses glucagon secretion from alpha cells is unknown. In this study, we show that insulin induces activation of GABAA receptors in the alpha cells by receptor translocation via an Akt kinase-dependent pathway. This leads to membrane hyperpolarization in the alpha cells and, ultimately, suppression of glucagon secretion. We propose that defects in this pathway(s) contribute to diabetic hyperglycemia.

Aims/hypothesis: The role of gamma-aminobutyric acid (GABA) and A-type GABA receptors (GABA A Rs) in modulating islet endocrine function has been actively investigated since the identification of GABA and GABA A Rs in the pancreatic islets. However, the reported effects of GABA A R activation on insulin secretion from islet beta cells have been controversial. Methods: This study examined the hypothesis that the effect of GABA on beta cell insulin secretion is dependent on glucose concentration. Results: Perforated patchclamp recordings in INS-1 cells demonstrated that GABA, at concentrations ranging from 1 to 1,000 μmol/l, induced a transmembrane current (I GABA ) which was sensitive to the GABA A R antagonist bicuculline. The current-voltage relationship revealed that I GABA reversed at −42±2.2 mV, independently of glucose concentration. Nevertheless, the glucose concentration critically controlled the membrane potential (V M ), i.e., at low glucose (0 or 2.8 mmol/l) the endogenous V M of INS-1 cells was below the I GABA reversal potential and at high glucose (16.7 or 28 mmol/l), the endogenous V M of INS-1 cells was above the I GABA reversal potential. Therefore, GABA dose-dependently induced membrane depolarisation at a low glucose concentration, but hyperpolarisation at a high glucose concentration. Consistent with electrophysiological findings, insulin secretion assays demonstrated that at 2.8 mmol/l glucose, GABA increased insulin secretion in a dose-dependent fashion (p<0.05, n=7). This enhancement was blocked by bicuculline (p<0.05, n=4). In contrast, in the presence of 28 mmol/l glucose, GABA suppressed the secretion of insulin (p<0.05, n=5). Conclusions/interpretation: These findings indicate that activation of GABA A Rs in beta cells regulates insulin secretion in concert with changes in glucose levels.

A simple and efficient approach for profiling the greenness of high performance liquid chromatography (HPLC) methods is presented. This environmental assessment tool (EAT) takes into consideration the environmental, health and safety issues for all solvents involved in the chromatographic method, and calculates a total score that can be used for comparison of the greenness of different methods. A software, HPLC-EAT, has been designed to facilitate the calculation and can be downloaded free of charge at http://www.biotek.lu.se/hplc-eat/. HPLC-EAT was successfully applied for a set of different HPLC methods from the literature, including both analytical and preparative chromatography. The performance of the tool was validated and it was further combined with another free software Eco-solvent tool to perform life cycle assessments of waste disposal options of distillation or incineration. HPLC-EAT can be routinely used in method development to calculate the greenness beside the conventional standards of accuracy, robustness and reproducibility.Although analytical chemists have considered environmental improvements important for a long time, the interest for green analytical chemistry has exploded during the last few years, as evident, for example, from the large number of publications and the special issue devoted to this subject by Trends in Analytical Chemistry (2010, volume 29, issue 7). 1-5 Green analytical chemistry goes hand in hand with the wellknown concept of green chemistry, 6,7 and can be summarized by