Effect of osmotic changes on intracellular pH and haemoglobin oxygen affinity of human erythrocytes

The effect of osmolality on intra-erythrocytic pH and haemoglobin oxygen affinity of red cells was studied at three different osmolality levels (the mean osmolalities were respectively 257, 294 and 341 mOsmol). No osmotically induced alteration of the pHe-pHi relationship was observed. In contrast, P50(7.4) increased (namely: 24.5, 24.9 and 25.6 torr) as osmolality rose. This increase was accompanied by a simultaneous increment of both MCHC (respectively 30.5, 33.4 and 36.3 g percent) and 2,3-DPG concentration (4.495, 4.924 and 5.392 mM/l red cells) while the 2,3-DPG/Hb molar ratio remained constant. The different factors that might induce such a change in haemoglobin affinity for oxygen were discussed. It would be best explained by a modification in the amount of haemoglobin-bound 2,3-DPG when 2,3-DPG and haemoglobin concentrations in red cell vary simultaneously.