AJP - Regulatory, Integrative and Comparative Physiology, Vol 258, Issue 3 711-R717, Copyright © 1990 by American Physiological Society
Regulation of glycolysis in the pectoralis muscles of seasonally acclimatized American goldfinches exposed to cold
R. L. Marsh, W. R. Dawson, J. J. Camilliere and J. M. Olson
Department of Biology, Northeastern University, Boston, Massachusetts 02115.
Regulation of glycolysis was assessed in winter- and summer-acclimatized
goldfinches (Carduelis tristis). We exposed birds to a thermo-neutral
temperature (30 degrees C), moderate cold (-15 degrees C), and severe cold
(0 degrees C in an atmosphere of 21% O2-79% He), and then measured
concentrations of glycogen, glycolytic intermediates, and citrate in the
pectoralis muscles. Winter birds used less glycogen when exposed to
moderate cold than did summer birds, confirming the carbohydrate sparing
noted by Marsh and Dawson [Am. J. Physiol. 242 (Regulatory Integrative
Comp. Physiol. 11): R563-R569, 1982]. However, depletion of muscle glycogen
did not correlate with thermoregulatory failure in this study.
Concentrations of glucose 6-phosphate and fructose 6-phosphate in the
pectoralis muscles were approximately 1.9 and 0.3 mumol/g wet mass in birds
exposed to thermoneutral temperatures. The levels of these intermediates
fell 50-70% under conditions known to enhance flux through glycolysis as
indicated by increased glucose turnover and glycogen depletion. This
information identifies phosphofructokinase (PFK) as a major regulated step
in glycolysis in these highly aerobic skeletal muscles. Winter birds
maintained the inhibition of this step under conditions of moderate cold.
However, concentrations of citrate, which have been hypothesized to be an
important inhibitor of PFK, did not correlate with the observed pattern of
inhibition. Therefore, if the enhanced beta-oxidative capacity of winter
birds is important in the regulation of glycolysis, a mechanism other than
the accumulation of citrate may be involved.
