CO(2) permeability of the rat erythrocyte membrane and its inhibition

We have studied the CO(2) permeability of the erythrocyte membrane of the rat using a mass spectrometric method that employs (18 )O-labelled CO(2). The method yields, in addition, the intraerythrocytic carbonic anhydrase activity and the membrane HCO(3)(−) permeability. For normal rat erythrocytes, we find at 37 °C a CO(2) permeability of 0.078 ± 0.015 cm/s, an intracellular carbonic anhydrase activity of 64,100, and a bicarbonate permeability of 2.1 × 10(−3 )cm/s. We studied whether the rat erythrocyte membrane possesses protein CO(2) channels similar to the human red cell membrane by applying the potential CO(2) channel inhibitors pCMBS, Dibac, phloretin, and DIDS. Phloretin and DIDS were able to reduce the CO(2) permeability by up to 50%. Since these effects cannot be attributed to the lipid part of the membrane, we conclude that the rat erythrocyte membrane is equipped with protein CO(2) channels that are responsible for at least 50% of its CO(2) permeability.