Membrane fluidity gradient model of cell transport

A new model of cellular transport is presented, characterized by selective fluxes due to membrane fluidity gradient. This mechanism is treated in terms of the interfacial tensions at the membrane/cytoplasm and membrane/medium surfaces. A higher interior fluidity (lower interfacial tension) is maintained by cytoplasm adenosine triphosphate, which adsorbs and increases lipoprotein fluidity while it also chelates calcium and keeps it from inner membrane sites. The high medium calcium causes a stiffer membrane (higher interfacial tension) on the medium side. These two different free energy barriers at inner and outer channel mouths filter all molecules, whether ionized or nonelectrolytic. Molecules with excess of hydrophobic groups, which makes negative the free energy of transfer from the medium into the membrane, have highest influx. Intermolecular salt linkages and hydrogen-bonding are vital in making negative the free energy of transfer of amino acids and sugars. The much lower energy barrier at the cytoplasmic interface favors net efflux from the cell of the more polar ions and amphipaths. Intramembrane particles are proposed as the channel sites.