First apparent dissociation constant of carbonic acid, pK'1, of plasma and erythrocytes.

The first apparent dissociation constant of carbonic acid, pK'1, of plasma and red cells was determined on venous blood of ten healthy, adult, male, human subjects. pH and PCO2 of plasma and red cells were analyzed electrometrically and a micromanometric method was used for the determination of total carbon dioxide content. Erythrocyte carbamino hemoglobin levels were estimated and used for the correction of erythrocyte pK'1. Each blood sample was subjected to the following regimen before centrifugation, 1) As drawn from the antecubital vein, 2) Oxygenated with a 5% CO2, O2 balance gas mixture, and 3) Reduced with a 5% CO2, N2 balance gas mixture. pK'1 of plasma and red cells are presented: (see article). The consistently larger values for red cell pK'1 than the respective plasma data may be attributed to the greater amount of carbamino hemoglobin concentration present in the erythrocytes. A simplified method for the calculation of erythrocyte bicarbonate concentration using the experimentally determined red cell pK'1 value has been formulated. The method involves the use of a regression equation relating plasma and red cell pH, the equivalence of plasma and red cell PCO2, along with the experimentally determined red cell pK'1.