ABSTRACT Rainbow smelt (Osmerus mordax) is a small fish that accumulates glycerol at low winter sea water temperatures. In laboratory held fish, glycerol concentration typically reaches 225 mM in plasma and in all cells. Glycerol uptake by heart and red blood cells (RBCs) was assessed by tracking [14C(U)]-glycerol into the acid soluble pool. In fish acclimated to 9-10°C a decrease in perfusion/incubation temperature from 8 to 1°C resulted in a decrease in glycerol uptake with a Q10 of 3.2 in heart and 2.4 in RBCs. Acclimation to ~1.5°C did not result in an adaptive enhancement of glycerol uptake as rates were unchanged in heart and RBCs. Glycerol uptake at 1°C was by passive diffusion in heart as evidenced by a linear relationship between glycerol uptake and extracellular glycerol concentration and a lack of inhibition by phloretin. In contrast, in RBCs, glycerol uptake with respect to glycerol concentration showed two linear relationships with a transition point around 50 mM extracellular glycerol. The slope of the second phase was much steeper and eliminated with the inclusion of phloretin. In RBCs from Atlantic salmon (Salmo salar), a related species that does not accumulate glycerol, glycerol uptake showed only a single linear curve and was not inhibited by phloretin. The data imply a strong facilitated component to glycerol uptake in rainbow smelt RBCs at high glycerol concentrations. We propose this is related to cyclic changes in RBC glycerol content involving a loss of glycerol at the gill and a re-accumulation during passage through the liver.
- low temperature
- Copyright © 2011, American Journal of Physiology - Regulatory, Integrative and Comparative Physiology