Abstract
Many 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 O2 off-loading from mouse RBCs, we now report that most O2 traverses membrane-protein channels. Two agents excluded from the RBC interior markedly slow O2 off-loading: p-chloromercuribenzenesulfonate (pCMBS) reduces inferred membrane O2 permeability (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) reduces PMembrane by ∼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 O2 channels and pointing to the existence of other O2 channel(s), all of which could be subject to physiological regulation and pharmacological intervention, our work represents a paradigm shift for O2 handling.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
Title Page: Added Gerolf Gros as an author and added affiliation Page 1: through the to the bulk extracellular... is fixed to to the bulk extracellular... Page 2 in paragraph 1: more that diffusion through... is fixed to more than diffusion through... Page 9: Reprints and permissions information is available at www.nature.com/reprints is deleted in author information. End Notes: Removed Gerolf Gros from acknowledgements and added Gerolf Gros author contribution.
