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

Abstract

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, P_O2, of AQP1-deficient (Colton Null) with that of normal human red cell membranes, 2) compare the P_O2 of Aqp1-/- with that of normal mouse red cells, 3) study the effect of the gas channel inhibitor DIDS on P_O2 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 P_O2, by 20% in human and by 37% in mouse red cells. DIDS causes reductions in P_O2 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 P_O2 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.