title: The effect of glucagon on the kinetics of hepatic mitochondrial calcium uptake.
abstract: Previous work by this and other laboratories has shown that glucagon administration stimulates calcium uptake by subsequently isolated hepatic mitochondria. This stimulation of hepatic mitochondrial Ca2+ uptake by in vivo administration of glucagon was further characterized in the present report. Maximal stimulation of mitochondrial Ca2+ accumulation was achieved between 6-10 min after the intravenous injection of glucagon into intact rats. Under control conditions, Ca2+ uptake was inhibited by the presence of Mg2+ in the incubation medium. Glucagon treatment, however, appeared to obliterate the observed inhibition by Mg2+ of mitochondrial Ca2+ uptake. Kinetic experiments revealed the usual sigmoidicity associated  with initial velocity curves for mitochondrial calcium uptake. Glucagon treatment did not alter this sigmoidal relationship. Glucagon treatment significantly increased the V max for Ca2+ uptake from 292 +/- 22 to 377 +/- 34 nmoles Ca2+/min per mg protein (n = 8) but did not affect the K 0.5, (6.5-8.6 microM). Since the major kinetic change in mitochondrial Ca2+ uptake evoked by glucagon is an increase in V max, the enhancement mechanism is likely to be an increase either in the number of active transport sites available to Ca2+ or in the rate of Ca2+ carrier movement across the mitochondrial membranes.
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002118:Calcium / Q000378:metabolism*; D005934:Glucagon / Q000494:pharmacology*; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D015636:Magnesium Chloride; D008297:Male; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism*; D051381:Rats
chemical_list: D015636:Magnesium Chloride; D005934:Glucagon; D008274:Magnesium; D002118:Calcium