Electrical Potentials during Carbon Dioxide Transport in Hemoglobin Solutions

Abstract

Transport of CO₂ in aqueous solutions is enhanced by the diffusion of HCO₃ ions (Gros and Moll, 1971, 1974). This facilitated transport is dependent on the kinetics of CO₂ hydration (Enns, 1976; Otto and Quinn,1971) and therefore on the concentration of carbonic anhydrase (CA). The role of charged proteins, if present in the solution, has remained unclear. It was suggested in the case of albumin that the protein serves mainly as a carrier of protons (Gros and Moll, 1974). However, since the macromolecules are nearly immobile, compared to the smaller bicarbonate ions, appreciable diffusion potentials can be generated by the imposition of a CO₂ gradient across a protein solution. These electrical potentials can significantly affect the facilitated CO₂ transport. An analysis which accounts for electrical potentials does in fact provide the explanation for what must be regarded as a relatively low permeability of CO₂ in protein solutions (Meldon, 1975). We report here experimental results which demonstrate the induction of sizable diffusion potentials by the transport of CO₂ in hemoglobin solutions, and describe the influence of these potentials on CO₂ transport.