gramicidin-a and alpha-cyano-4-hydroxycinnamate

The different roles of glycolytic and mitochondrial pathways in glucose-induced metabolic activation and insulin secretion were studied in islets of Langerhans. Single islets were perifused with 3 mM glucose together with agents affecting the production or consumption of ATP. Subsequently, glucose was raised to 11 mM and the effects of the agents on metabolic and secretory responses were evaluated. Metabolism was monitored continuously with an oxygen-sensitive microelectrode inserted into the islet. Insulin secretion was determined by assaying insulin in perifusate with ELISA. Inhibitors of mitochondrial ATP production reduced the metabolic and secretory response to glucose. When glycolytic ATP production was reduced, initial but not sustained glucose-stimulated insulin release was observed. Inhibition of mitochondrial pyruvate transport reduced the glucose-induced decline in pO(2). Although mitochondrial metabolism was eventually similar to normal, insulin release was only 20% of normal. Increased energy expenditure also changed the kinetics of the glucose-induced decline in pO(2) and decreased the insulin release by 50%. In conclusion, glucose-induced enhancement of insulin release was only seen when the rise of the sugar concentration triggered a rapid and sustained increase of mitochondrial metabolism. This activation of mitochondrial metabolism required a good metabolic state prior to the glucose challenge.

Topics: Animals; Arsenates; Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; Cell Respiration; Cells, Cultured; Chelating Agents; Coumaric Acids; Egtazic Acid; Enzyme Inhibitors; Enzyme-Linked Immunosorbent Assay; Glucose; Glycolysis; Gramicidin; Insulin; Insulin Secretion; Islets of Langerhans; Male; Mice; Microelectrodes; Mitochondria; Oligomycins; Ouabain; Oxidative Phosphorylation; Oxygen; Uncoupling Agents

A compact, laser desorption tandem time-of-flight mass spectrometer is described. The instrument incorporates two dual-stage reflectron analyzers and a collision region for producing product ions by collision-induced dissociation. Selection of ions of a particular mass is accomplished by deflection of ions from stable trajectory angles entering the second reflectron, while the use of a pulsed valve for introduction of the collision gas obviates the need for differential pumping of the collision region. Initial results are presented, as well as a discussion for optimizing the performance of tandem time-of-flight instruments.

Topics: Coumaric Acids; Gramicidin; Mass Spectrometry; Rhodamines