Electrical impedance tomography study of biological processes in a single cell

An in vivo electrical impedance tomography (EIT) study of single plant cells of Chara corallina is reported. When these aquatic cells grow in alkaline conditions, proton-translocating ATP synthases in the plasma membrane operate in reverse, utilizing ATP to translocate protons against an electrochemical gradient to the periplasm and creating localized acidic regions along the cell's cylindrical surface. These acidic regions, which appear as radial bands, approximately 5 mm long, between narrower alkaline bands, facilitate the uptake of bicarbonate, the plant's source of inorganic carbon for photosynthesis in the carbon dioxide-depleted alkaline conditions. Our EIT study of cell ultrastructure in the acidic and alkaline regions provides evidence that the plasma membrane is folded in localized regions (e.g., charasomes) in the acidic bands. The very low frequency capacitance dispersions were very similar to those of double fixed-charge structures. Such charge distributions are known to be present in the membrane-bound F0 portion of the ATP synthase. The theoretical dependence of the fixed-charge concentrations on pH in the proteins is shown to broadly account for the observed correlations between pH, membrane potential, conductance, and capacitance in these regions. In synthetically formed double fixed-charge membranes, electric field-induced dissociation of water into H+ and OH- occurs. This leads to the speculation that H+/OH- fluxes in ATP synthases located in the alkaline regions of Chara cells might also involve the electric field-induced dissociation of water.