CARBON-DIOXIDE TRANSPORT IN ALLIGATOR BLOOD AND ITS ERYTHROCYTE PERMEABILITY TO ANIONS AND WATER

Deoxygenation of alligator red blood cells (RBCs) caused binding of tw o HCO3- equivalents per hemoglobin (Hb) tetramer at physiological pH. At lowered pH, some HCO3- binding also occurred to oxygenated Hb. The erythrocytic total CO2 content was large, and Hb-bound HCO3-, free HCO 3-, and carbamate contributed about equally in deoxygenated cells. The nonbicarbonate buffer values of RBCs and Hb were high, and the Hb sho wed a significant fixed acid Haldane effect. Binding of HCO3- on deoxy genation occurred without a change in RBC intracellular pH, revealing equivalence between oxylabile HCO3- and H+ binding. Erythrocyte volume , plasma pH, and plasma HCO3- concentration also varied little with th e degree of oxygenation. Diffusional water permeability was higher in oxygenated than deoxygenated RBCs. The RBCs have rapid band 3-mediated Cl- and HCO3- transport, which was not affected by degree of oxygenat ion, but net fluxes of Cl- and HCO3- via the anion exchanger are small during blood circulation at rest. Most of the CO2 taken up into the b lood as it flows through tissue capillaries is carried within the eryt hrocytes as Hb-bound HCO3- until CO2 is excreted when blood flows thro ugh pulmonary capillaries.