Effects of oxygen saturation on the CO2 transport properties of Lampetra red cells

We investigated the effects of haemoglobin oxygenation on the carbon dioxide transport properties of lamprey (Lampetra fluviatilis) erythrocytes. The non-bicarbonate buffering capacity of deoxygenated lamprey erythrocytes was -43 mmol.L-1.pH unit-1. The carbon dioxide content of oxygenated erythrocytes was 7-8 mM lower than that of deoxygenated erythrocytes over a range of carbon dioxide tensions. This was the result of a pronounced Haldane effect (proton uptake by haemoglobin upon deoxygenation): at extracellular pH 7.5, the intracellular pH of oxygenated erythrocytes was 7.67, and increased to 7.91 when the haemoglobin-oxygen saturation decreased to 7%. No specific oxylabile binding of bicarbonate or carbon dioxide to haemoglobin occurred under the conditions of the present study. Owing to the high red cell pH and its large increase upon deoxygenation, carbon dioxide can be effectively transported in lamprey blood, although plasma bicarbonate is not available for carbon dioxide excretion because of the lack of rapid anion exchange across the red cell membrane.