Vol. 275, Issue 3, R818-R823, September 1998
No evidence for homeoviscous adaptation in a heterothermic
tissue: tuna heat exchangers
Douglas S.
Fudge,
E. Don
Stevens, and
James S.
Ballantyne
Department of Zoology, University of Guelph, Guelph, Ontario, Canada
N1G 2W1
Many poikilotherms are known to adjust the
membrane composition of their cells in response to a temperature change
so that membrane fluidity, and therefore function, is conserved. Such compensatory changes in membrane composition are considered
"homeoviscous adaptations." In this study, we examined a
heterothermic tissue, the visceral rete mirabile of the bluefin tuna,
for evidence of homeoviscous adaptation. We measured the proportions of
phospholipid fatty acids and phospholipid head groups as a function of
position along the rete thermal gradient, which has been estimated to
be ~10°C. We found no effect of position along the rete on the
composition of either phospholipid fatty acids or head groups. Our
results were unexpected in light of our previous demonstration of
compensation of metabolic enzyme activity in the same tissue. The lack
of evidence for a homeoviscous response may be due to the fluctuating
nature of the thermal gradient along the visceral retia; i.e.,
membranes may be adapted to a eurythermal existence rather than being
fine-tuned to a particular temperature.
Thunnus; bluefin; temperature; rete mirabile; endothermy
