Causes of the differences in respiration rate of hepatocytes from
mammals of different body mass.
Porter, R. K. & Brand, M. D.
Department of Biochemistry, University of Cambridge, Tennis Court
Road, Cambridge CB2 1QW, UK
APStracts 2:0183R, 1995.
Resting oxygen consumption of hepatocytes isolated from mammals
ranging in mass from 20g mice to 200kg horses, decreases with
increasing body mass. The substrate oxidation system increases in
activity with increasing body mass and mitochondrial proton leak and
phosphorylation system decrease in activity, resulting in a higher
mitochondrial membrane potential in hepatocytes from larger mammals.
The absolute rates of oxygen consumption due to non-mitochondrial
processes, substrate oxidation, mitochondrial proton leak and the
phosphorylation system all decrease with increasing body mass. These
decreases are due partly to a decrease in mitochondrial number per
cell and partly to decreases in mitochondrial inner membrane proton
leakiness and in ATP turnover by cells from larger mammals.
Quantitatively, the proportion of total cell oxygen consumption by
non-mitochondrial processes (13%) and oxidation of substrates (87%)
and the proportions used to drive mitochondrial proton leak (19%) and
the phosphorylation system (68%) are the same for hepatocytes from
all mammals investigated. The effect of matched decreases in the
rates of proton leak and of ATP turnover is to keep the effective P/O
ratio relatively constant with body mass, suggesting that the
observed value is optimal.
Received 21 October 1994; accepted in final form 13 June 1995.
APS Manuscript Number R610-4.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 11 July 1995.