Selective stimulation of in situ intermediary metabolism by free calcium in permeabilized rat adipocytes.
The hypothesis that ionized calcium [Ca2+]i may stimulate in situ rat adipocyte intermediary metabolism distal to glucose transport was tested. A metabolically active porous adipocyte model was employed in which pathway metabolism is exclusively pore-dependent using glucose 6-phosphate (G6P) as substrate. Cellular [Ca2+]i was, furthermore, directly adjusted to between 0-2.5 microM via the membrane pores. Three metabolic fluxes were examined, (1) glycolysis-Krebs ([6-14C]G6P oxidation), (2) glycolysis to lactate ([U-14C]G6P to [14C]lactate) and (3) pentose pathway ([1-14C]G6P oxidation). Glycolysis-Krebs oxidation was was found to be selectively (33% above basal P less than 0.001) stimulated by 0.625 microM free calcium. In contrast, there was no effect of [Ca2+]i on the other, exclusively cytoplasmic, pathways. The stimulation of glycolysis-Krebs by [Ca2+]i was inhibited by a mitochondrial calcium channel blocker (Ruthenium red) and persisted over a range of ATP/ADP ratios. Separate studies demonstrated that 2-[1-14C]ketoglutarate oxidation was also calcium-stimulated in the porous adipocytes (160% over baseline at 1 microM [Ca2+]i). These studies thus demonstrate that physiologically relevant increments in porous adipocyte [Ca2+]i enhance overall in situ glycolytic-Krebs pathway oxidation by a mechanism which entails mitochondrial calcium uptake. Methodologically, this metabolically active porous adipocyte model presents a novel experimental approach to investigations regarding the effects of ionized calcium on intermediary metabolism beyond glucose transport.
Mick
G J
GJ
Department of Pediatrics, SUNY College of Medicine, Syracuse 13210.
Lee
J
J
McCormick
K L
KL
D000273:Adipose Tissue / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002952:Citric Acid Cycle / Q000502:physiology; D003593:Cytoplasm / Q000378:metabolism; D019298:Glucose-6-Phosphate; D005958:Glucosephosphates / Q000378:metabolism*; D006019:Glycolysis / Q000502:physiology; D007477:Ions; D007656:Ketoglutaric Acids / Q000378:metabolism; D008297:Male; D008928:Mitochondria / Q000378:metabolism; D010427:Pentose Phosphate Pathway / Q000502:physiology; D051381:Rats; D012430:Ruthenium Red / Q000378:metabolism
D005958:Glucosephosphates; D007477:Ions; D007656:Ketoglutaric Acids; D012430:Ruthenium Red; D019298:Glucose-6-Phosphate; D002118:Calcium