THE COUPLING OF METABOLIC TO SECRETORY EVENTS IN PANCREATIC-ISLETS - GLUCOSE-INDUCED CHANGES IN MITOCHONDRIAL REDOX STATE

Mitochondrial NAD(+), NADH, NADP(+) and NADPH were measured in dispers ed pancreatic islet cells incubated in the absence or presence of D-gl ucose and then exposed for 20 s to 0.5 mg/ml digitonin. The latter tre atment resulted in the full release of lactate dehydrogenase without a ny detectable loss of glutamate dehydrogenase. The permeabilized cells were separated from the incubation medium by centrifugation through a n oil layer and their content in pyridine nucleotides measured by a ra dioisotopic procedure coupled to the classical cycling technique. Rela tive to basal value, D-glucose, in concentrations of 2.8 and 16.7 mM, caused a concentration-related increase in both the NADH/NAD(+) and NA DPH/NADP(+) ratio. These findings provide the first direct evidence fo r the induction of a more reduced mitochondrial redox state in glucose -stimulated pancreatic islets.