The permeability of human red blood cell membranes to hydrogen peroxide is independent of aquaporins

Hydrogen peroxide (H(2)O(2)) not only is an oxidant but also is an important signaling molecule in vascular biology, mediating several physiological functions. Red blood cells (RBCs) have been proposed to be the primary sink of H(2)O(2) in the vasculature because they are the main cellular component of blood with a robust antioxidant defense and a high membrane permeability. However, the exact permeability of human RBC to H(2)O(2) is neither known nor is it known if the mechanism of permeation involves the lipid fraction or protein channels. To gain insight into the permeability process, we measured the partition constant of H(2)O(2) between water and octanol or hexadecane using a novel double-partition method. Our results indicated that there is a large thermodynamic barrier to H(2)O(2) permeation. The permeability coefficient of H(2)O(2) through phospholipid membranes containing cholesterol with saturated or unsaturated acyl chains was determined to be 4 × 10(−4) and 5 × 10(−3) cm s(−1), respectively, at 37 °C. The permeability coefficient of human RBC membranes to H(2)O(2) at 37 °C, on the other hand, was 1.6 × 10(−3) cm s(−1). Different aquaporin-1 and aquaporin-3 inhibitors proved to have no effect on the permeation of H(2)O(2). Moreover, human RBCs devoid of either aquaporin-1 or aquaporin-3 were equally permeable to H(2)O(2) as normal human RBCs. Therefore, these results indicate that H(2)O(2) does not diffuse into RBCs through aquaporins but rather through the lipid fraction or a still unidentified membrane protein.