Aquaporin-1 acts as an O2 channel. The permeability of human and mouse red cell membranes for oxygen

It has been demonstrated that aquaporin-1 (AQP1), one of the most abundant red cell membrane proteins, constitutes a functionally important channel for CO2 in red cell membranes. We ask here, whether AQP1 and other gas channel proteins play a role also in red cell oxygen transport. We use a stopped-flow technique to: 1) compare the oxygen permeability, PO2, of AQP1-deficient (Colton Null) with that of normal human red cell membranes, 2) compare the PO2 of Aqp1-/- with that of normal mouse red cells, 3) study the effect of the gas channel inhibitor DIDS on PO2 of human and mouse red cells, and 4) investigate all three effects at various temperatures between 7 and 37°C, because O2 transfer across channels and across membrane lipids may depend differently on temperature. We find that at 7°/10°C lack of AQP1 in the red cell membrane causes significant reductions of PO2, by 20% in human and by 37% in mouse red cells. DIDS causes reductions in PO2 by 34% in human and by 88% in mouse red cells. In addition, the AQP1 inhibitor 5-(phenoxymethyl)furan-2-carbaldehyde) (5-PMFC) decreases human red cell PO2 by ~40%. All these effects are highly visible at 7/10°C, but minor or absent at 25°C and 37°C, suggesting that O2 passage through the channel(s) increases less with temperature than O2 permeation through membrane lipids. Lack of AQP1 and exposure to DIDS or 5-PMFC indicate that AQP1 – possibly along with other gas channels – at <25°C acts as an efficient channel for O2.