J. Biol. Chem., Vol. 263, Issue 12, 5700-5706, 04, 1988
Hormonal regulation of the alpha-ketoglutarate dehydrogenase complex in the isolated perfused rat liver
HM Rashed, FM Waller and TB Patel
Department of Pharmacology, University of Tennessee, Memphis 38163.
The metabolic flux through the alpha-ketoglutarate dehydrogenase reaction
in perfused livers was monitored by measuring the rate of 14CO2 production
from [1-14C]alpha-ketoglutarate. The rates of 14CO2 production and glucose
production from [1-14C]alpha-ketoglutarate were increased with increasing
perfusate alpha-ketoglutarate concentrations. Vasopressin, angiotensin II,
and the alpha 1-adrenergic agonist phenylephrine stimulated transiently by
2.5-fold the metabolic flux through the alpha-ketoglutarate dehydrogenase
reaction in the presence and absence of Ca2+ in the perfusion medium. High
concentrations of glucagon (1 x 10(-8) M) and 8-p-chlorophenylthio-cAMP
(100 microM) (data not shown) also stimulated transiently the metabolic
flux through the alpha-ketoglutarate dehydrogenase reaction. However, lower
glucagon concentrations (1 x 10(-9) M) stimulated the rate of 14CO2
production from [1-14C]alpha-ketoglutarate only under conditions optimized
to fix the cellular oxidation-reduction state at an intermediate level,
when glucagon (1 x 10(-9) M)-mediated elevation of cAMP content was greater
than that observed under highly oxidizing and reducing conditions. These
data indicate that agonists which increase cytosolic free Ca2+ levels
stimulate the metabolic flux through the alpha-ketoglutarate dehydrogenase
complex. Furthermore, the data presented here demonstrate for the first
time that physiological glucagon concentrations stimulate the metabolic
flux through the alpha-ketoglutarate dehydrogenase reaction only under
conditions known to be optimal for glucagon- mediated Ca2+ mobilization in
the isolated perfused rat liver.