Physiology of ionophore transport of potassium and sodium ions across cell membranes: valinomycin and 18-crown-6 ether

The processes involved in transport of K and Na by the carrier ionophores valinomycin and 18-crown-6 ether across cell membranes have been elucidated using quantum mechanical modelling: 1. Formation of the {ionophore-M} complex: desolvation (ΔGdesolv) of the central cavity of the ionophore, change in configurational energy TΔS, desolvation of the M(H2O)6-7 + 2. Desolvation of the {ionophore-M} complex prior to entering the membrane environment 3. Permeation through the lipophilic environment of the membrane, which is dependent on the lipophilicity (ΔGlipo), dipole moment μ, and molecular volume of the {ionophore-M } complex. 4. Release of the M on the intracellular side, and diffusion of the free ionophore back towards the extracellular side to restart the process. Results from this study show that it is possible to design molecular structures to enhance the ability of crown ethers to selectively transport alkali metal ions across lipid membranes.