Catecholamine-induced changes in oxygen affinity of carp and trout blood

Carp and trout blood maintained at low constant oxygen and carbon dioxide tensions was β-stimulated. This activated the Na+H+-exchanger of the red cell membrane, leading to increases in red cell pH (pHi) and cell water content, the latter resulting in dilution of hemoglobin and organic phosphates. The increase in pHi was rapid and maintained throughout the experimental period, the trout red cells showing the largest increase. Likewise swelling of the red cells was larger in trout than in carp blood. As a consequence of β-stimulation the oxygen affinity of the blood increased. In trout the intracellular Bohr factor of unstimulated blood combined with the pHi increase upon stimulation could account for 85% of the increase in oxygen affinity, whereas it only covered 65% of the increase in carp blood. We therefore conclude that blood oxygen affinity is dependent on the red cell hemoglobin concentration in both species, the effect being more marked in carp.