AJP - Regulatory, Integrative and Comparative Physiology, Vol 265, Issue 1 41-R48, Copyright © 1993 by American Physiological Society
Response of protein synthesis to anoxia and recovery in anoxia-tolerant hepatocytes
S. C. Land, L. T. Buck and P. W. Hochachka
Department of Zoology, University of British Columbia, Vancouver, Canada.
Hepatocytes from the western painted turtle (Chrysemys picta bellii)
display a profound metabolic suppression under anoxia. Fractional rates of
protein synthesis fell by 92% during 12 h anoxia at 25 degrees C and were
indistinguishable from the rate obtained with cycloheximide. Normoxic
recovery saw protein synthesis increase to 160% of control values and
return to normal after 2 h. The GTP-to-GDP ratio, implicated in the control
of translation, fell threefold during anoxia. Purine nucleotide phosphate
profiles suggest that this change occurs through increasing concentrations
of ADP and GDP, with concentrations of ATP and GTP and total purines
remaining constant. The normoxic cost for protein synthesis was calculated
at 47.6 +/- 6.8 mmol ATP/g protein. Normoxic protein synthesis accounted
for 36% of overall ATP turnover rates, close to the extent of O2
consumption inhibitable by cycloheximide (28%). Under anoxia, the
proportion of ATP turnover utilized by protein synthesis did not change
significantly. ATP turnover rates for urea synthesis reflected a similar
pattern, falling 72% under anoxia. These results reflect the cell's ability
to suppress protein synthesis under anoxia in a manner that is coordinated
with the reduction in total metabolic rate.
