No evidence for homeoviscous adaptation in a ...



Title No evidence for homeoviscous adaptation in a heterothermic tissue: tuna heat exchangers
Author(s) D. S. Fudge, E. D. Stevens, J. S. Ballantyne
Journal American Journal of Physiology-Regulatory Integrative and Comparative Physiology
Date 1998
Volume 275
Issue 3
Start page R818
End page R823
Abstract 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 "homeovvscous 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 similar to 10 degrees 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.

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