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. 2017 Jun 8;31(10):4256–4264. doi: 10.1096/fj.201601282R

Figure 6.

Figure 6.

A proposed model describes the mobile localization of AQP1 relative to band 3 on human erythrocyte membrane. Arrows: the main direction of fluxes of ions, water, and CO2 across the human RBC membrane. Band 3, which transports HCO3− across the cell membrane and CAII, which facilitates CO2(g)/HCO3−(aq) conversion, are 2 core components of the CO2 transport metabolon. Left: when erythrocytes circulate and squeeze through systemic capillaries in as short a time as 50 ms (45), CO2 metabolite generated by tissues enters RBCs via diffusion (dashed arrow) and via passage through AQP1 (solid arrow), as indicated in the model (8–10, 46), Intracellular CO2 is converted into HCO3− by CAII. The other reaction product, H+, is stabilized by deoxyhemoglobin as O2 exits from the RBCs. In systemic capillaries, RBCs undergo rheological changes and increased intracellular CO2 conversion. Water channel AQP1 physically interacts with band 3/CAII complexes to facilitate hydration of CO2. Right: when erythrocytes leave systemic capillary beds, they resume cell shapes and volume with water influx. As erythrocytes circulate toward the lungs for CO2 expiration, blood HCO3− is converted into CO2 and H2O. When RBCs are well hydrated, AQP1 is segregated from band 3/CAII complexes.