Ionic equilibria in red blood cells of rainbow trout (Salmo gairdneri): Cl-, HCO-3 and H+.

The equilibrium distributions of H+, Cl- and HCO-3 between plasma and erythrocytes of rainbow trout (Salmo gairdneri) blood were determined as a function of plasma pH (pHe, 7.0-8.2), temperature (5-15 degrees C), and mode of blood acidification (CO2, HCl, lactic acid). The relationship between red cell pH (pHi) and pHe was not affected significantly by temperature or mode of blood acidification. H+, Cl- and HCO-3 were passively distributed across the red cell membrane as evidenced by the membrane's high permeability to Cl- and the similar Donnan ratios for H+ and Cl- at any given pHe. The relationship between pHe and the Donnan ratio for bound CO2 had a similar slope to the relationships between pHe and the Donnan H+ and Cl- ratios but was shifted upwards, presumably due to formation of carbamino compounds inside the red blood cell. This carbamino formation was enhanced at lower temperatures when blood pH was elevated.