Hexose metabolism in pancreatic islets. Participation of Ca2(+)-sensitive 2-ketoglutarate dehydrogenase in the regulation of mitochondrial function.
A rise in extracellular D-glucose concentration results in a preferential and Ca2(+)-dependent stimulation of mitochondrial oxidative events in pancreatic islet cells. The possible participation of Ca2(+)-dependent mitochondrial dehydrogenases, especially 2-ketoglutarate dehydrogenase, in such an unusual metabolic situation was explored in intact islets, islet homogenates and isolated islet mitochondria. In intact islets exposed to a high concentration of D-glucose, the removal of extracellular Ca2+ impaired D-[6-14C]glucose oxidation whilst failing to affect the cytosolic or mitochondrial ATP/ADP ratios. In islet homogenates, the activity of 2-ketoglutarate dehydrogenase displayed exquisite Ca2(+)-dependency, the presence of Ca2+ causing a 10-fold increase in affinity for 2-ketoglutarate. In intact islet mitochondria, the oxidation of 2-[1-14C]ketoglutarate also increased as a function of extramitochondrial Ca2+ availability. Moreover, prior stimulation of intact islets by D-glucose resulted in an increased capacity of mitochondria to oxidize 2-[1-14C]ketoglutarate. The absence of extracellular Ca2+ during the initial stimulation of intact islets impaired but did not entirely suppress such a memory phenomenon. It is proposed that the mitochondrial accumulation of Ca2+ in nutrient-stimulated islets indeed accounts, in part at least, for the preferential stimulation of mitochondrial oxidative events in this fuel-sensor organ.
Laboratory of Experimental Medicine, Brussels Free University, Belgium.
A
A
Sener
J
J
Rasschaert
W J
WJ
Malaisse
D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D003600:Cytosol / Q000378:metabolism; D005260:Female; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology; D006019:Glycolysis; D007515:Islets of Langerhans / Q000187:drug effects / Q000378:metabolism*; D007655:Ketoglutarate Dehydrogenase Complex / Q000378:metabolism*; D007658:Ketone Oxidoreductases / Q000378:metabolism*; D007700:Kinetics; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism*; D010085:Oxidative Phosphorylation / Q000187:drug effects*; D010101:Oxygen Consumption / Q000187:drug effects; D051381:Rats
D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D007658:Ketone Oxidoreductases; D007655:Ketoglutarate Dehydrogenase Complex; D005947:Glucose; D002118:Calcium