ABSTRACT
Unidirectional 36Cl− efflux via the red blood cell anion exchanger was measured under Cl− self-exchange conditions (i.e. no net flow of anions) in rainbow trout Oncorhynchus mykiss and red-eared freshwater turtle Trachemys scripta to examine the effects of acute temperature changes and acclimation temperature on this process. We also evaluated the possible adaptation of anion exchange to different temperature regimes by including our previously published data on other animals. An acute temperature increase caused a significant increase in the rate constant (k) for unidirectional Cl− efflux in rainbow trout and freshwater turtle. After 3 weeks of temperature acclimation, 5 °C-acclimated rainbow trout showed only marginally higher Cl− transport rates than 15 °C-acclimated trout when compared at the same temperature. Apparent activation energies for red blood cell Cl− exchange in trout and turtle were lower than values reported in endothermic animals. The Q10 for red blood cell anion exchange was 2.0 in trout and 2.3 in turtle, values close to those for CO2 excretion, suggesting that, in ectothermic animals, the temperature sensitivity of band-3-mediated anion exchange matches the temperature sensitivity of CO2 transport (where red blood cell Cl−/HCO3− exchange is a rate-limiting step). In endotherms, such as man and chicken, Q10 values for red blood cell anion exchange are considerably higher but are no obstacle to CO2 transport, because body temperature is normally kept constant at values at which anion exchange rates are high. When compared at constant temperature, red blood cell Cl− permeability shows large differences among species (trout, carp, eel, cod, turtle, alligator, chicken and man). Cl− permeabilities are, however, remarkable similar when compared at preferred body temperatures, suggesting an appropriate evolutionary adaptation of red blood cell anion exchange function to the different thermal niches occupied by animals.
