Carbon dioxide transport in alligator blood and its erythrocyte permeability to anions and water

Abstract

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