gramicidin-a and arsenic-acid

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

Isolated thylakoids were incubated for 14-16 h in the buffer containing 3-6 mCi T2O/ml and then resedimented and suspended in non-radioactive medium. It was found that illumination of thylakoids induced an increase in radioactivity level in CF1 isolated from these thylakoids. Such effect was observed only if photophosphorylation substrates (ADP and phosphate or arsenate) were added to the medium during illumination. The light-induced ADP and arsenate-dependent incorporation of tritium into CF1 was suppressed by DCCD and inhibited by low gramicidin concentrations to the same extent as photophosphorylation.

Topics: Adenosine Diphosphate; Arsenates; Chloroplasts; Dicyclohexylcarbodiimide; Gramicidin; Intracellular Membranes; Light; Photophosphorylation; Proton-Translocating ATPases; Tritium; Water

Respiration, membrane potential generation and motility of the marine alkalotolerant Vibrio alginolyticus were studied. Subbacterial vesicles competent in NADH oxidation and delta psi generation were obtained. The rate of NADH oxidation by the vesicles was stimulated by Na+ in a fashion specifically sensitive to submicromolar HQNO (2-heptyl-4-hydroxyquinoline N-oxide) concentrations. The same amounts of HQNO completely suppressed the delta psi generation. Delta psi was also inhibited by cyanide, gramicidin D and by CCCP + monensin. CCCP (carbonyl cyanide m-chlorophenylhydrazone) added without monensin exerted a much weaker effect on delta psi. Na+ was required to couple NADH oxidation with delta psi generation. These findings are in agreement with the data of Tokuda and Unemoto on Na+-motive NADH oxidase in V. alginolyticus. Motility of V. alginolyticus cells was shown to be (i) Na+-dependent, (ii) sensitive to CCCP + monensin combination, whereas CCCP and monensin, added separately, failed to paralyze the cells, (iii) sensitive to combined treatment by HQNO, cyanide or anaerobiosis and arsenate, whereas inhibition of respiration without arsenate resulted only in a partial suppression of motility. Artificially imposed delta pNa, i.e., addition of NaCl to the K+ -loaded cells paralyzed by HQNO + arsenate, was shown to initiate motility which persisted for several minutes. Monensin completely abolished the NaCl effect. Under the same conditions, respiration-supported motility was only slightly lowered by monensin. The artificially-imposed delta pH, i.e., acidification of the medium from pH 8.6 to 6.5 failed to activate motility. It is concluded that delta mu Na+ produced by (i) the respiratory chain and (ii) an arsenate-sensitive anaerobic mechanism (presumably by glycolysis + Na+ ATPase) can be consumed by an Na+ -motor responsible for motility of V. alginolyticus.

Topics: Arsenates; Carbonyl Cyanide m-Chlorophenyl Hydrazone; Cyanides; Electrophysiology; Gramicidin; Hydrogen-Ion Concentration; Hydroxyquinolines; Monensin; Movement; NAD; Oxidation-Reduction; Potassium; Sodium; Vibrio