Role of channels in the oxygen permeability of red blood cells

Abstract

AbstractMany have believed that oxygen (O2) crosses red blood cell (RBC) membranes by dissolving in lipids that offer no resistance to diffusion. However, using stopped-flow (SF) analyses of hemoglobin (Hb) absorbance spectra during O2off-loading from mouse RBCs, we now report that most O2traverses membrane-protein channels. Two agents excluded from the RBC interior markedly slow O2off-loading: p-chloromercuribenzenesulfonate (pCMBS) reduces inferred membrane O2permeability (PMembrane) by ∼82%, and 4,4’-diisothiocyanatostilbene-2,2’-disulfonate (DIDS), by ∼56%. Because neither likely produces these effects via membrane lipids, we examined RBCs from mice genetically deficient in aquaporin-1 (AQP1), the Rh complex (i.e., rhesus proteins RhAG + mRh), or both. The double knockout (dKO) reducesPMembraneby ∼55%, and pCMBS+dKO, by ∼91%. Proteomic analyses of RBC membranes, flow cytometry, hematology, and mathematical simulations rule out explanations involving other membrane proteins, RBC geometry, or extracellular unconvected fluid (EUF). By identifying the first two O2channels and pointing to the existence of other O2channel(s), all of which could be subject to physiological regulation and pharmacological intervention, our work represents a paradigm shift for O2handling.