Pronounced influence of Hb-O2 saturation on red cell pH in tench blood in vivo and in vitro.

At an extracellular pH of 7.9 the red cell pH in tench blood exhibits a nonlinear, strongly inverse relationship with Hb-O2 saturation, both when investigated in vitro and in vivo (in fish exposed to acid water with and without aluminium). The pHi difference between deoxygenated and oxygenated erythrocytes is large (i.e., 0.35 pH units), which can be accounted for by the Haldane effect and the buffering properties of the blood. The major shift in pHi occurs between 50 and 100% Hb-O2 saturation, indicating an almost full exploitation of the Haldane effect within the normal physiological range of blood O2 saturations.