Characterization of anion transport system in trout red blood cell

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Abstract
Anion transport in the trout red blood cell is mediated by a membrane protein that selectively binds dihydro-4,4'-dithiocyanostilbene-2,2'-disulfonic acid (3H2DIDS) and that forms on sodium dodecyl sulfate (SDS)-polyacrylamide gel electropherograms a band with the same diffuse structure at the same location as the band 3 protein of the mammalian red blood cells. There exists a linear relationship between binding of H2DIDS to this protein and the inhibition of anion equilibrium exchange. At maximal inhibition about 8 X 10(6) molecules/cell are bound to the protein. The kinetics of anion transport in the trout red blood cell differ from those of mammalian red blood cells. In addition to a H2DIDS-sensitive component of sulfate transport there exists a considerable H2DIDS-insensitive component with a relative magnitude that decreases with increasing temperature. At 23 degrees C, it amounts to about 25%. The temperature dependence of the H2DIDS-sensitive component is about 15 kcal/mol instead of 32 as in human red blood cells. Cl- transport increases with increasing pH. Above pH 7.4, the rate of transport becomes too fast to be measurable with either inhibitor stop or filtration technique. SO2-4 transport is nearly pH independent over the pH range 6.5 to 7.8 and the net entry of SO2-4 in exchange against intracellular Cl-, as followed in the absence of CO2, is accompanied by little if any proton uptake. Net proton uptake becomes measurable only at temperatures above 40 degrees C. Possibly at lower and more physiological temperatures, the band 3 protein in the red blood cell of the trout accomplishes part of the SO2-4 movements without cotransporting protons.