Continuous measurement of 13c16o2 production from 13c pyruvate by
intact liver mitochondria: effect of hco3-.
Ono, Y., L. Lin, B. T. Storey, Y. Taguchi, S. J. Dodgson, and R. E.
Forster.
Departments of Physiology and Obstetrics-Gynecology, School of
Medicine, University of Pennsylvania, Philadelphia, Pennsylvania
19104
APStracts 2:0276C, 1995.
We have measured continuously the production of mass 45 CO2 (13C16O2)
from 13C labelled pyruvate in a guinea pig liver mitochondrial
suspension and simultaneously the O2 consumption (O2) at 37 degrees C
and pH 7.4. The reactions took place in a closed, 3 ml volume,
stirred, thermoregulated chamber separated from the ion source of a
mass spectrometer by a gas permeable membrane which permitted
recording the mass peaks of any gas dissolved in the reaction mixture
with a response time as fast as 3 seconds. If the pyruvate was
labelled on carbon 2 no 13C16O2 was formed even after an hour
indicating the 2nd and 3rd carbons were not metabolized in the citric
acid cycle. We found that 13C16O2 was 5 times greater in the presence
of 25 mM HCO3- than in its absence. A probable mechanism of this
CO2/HCO3- effect is carboxylation of pyruvate to oxaloacetate which
would react with acetyl CoA to form citrate and with NADH to form
malate, thus removing two major inhibitors of pyruvate dehydrogenase.
We conclude that CO2/HCO3- has a potent and hitherto unappreciated
regulatory effect on liver pyruvate dehydrogenase.
Received 27 December 1994; accepted in final form 30 June 1995.
APS Manuscript Number C740-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 July 1995.