A physical model of potential energy profiles of ions going through a biological membrane channel

To attempt to explain what determines a single particle (an ion or an ion group) penetration of a cell membrane channel, a physical model of potential energy profiles V/sub 2/(x) of a channel is proposed, based on the authors' previous study of one dimensional (1-D) steady state Schrodinger equation in a single particle system and in a time independent field. In this model, a V/sub 2/(x) is simplified as an effective constant height of potential energy barrier V/sub 2/ in a channel to obtain analytical solutions in mathematics. This model elucidates that: (1) Ion selectivity of a channel is determined by V/sub 2/. V/sub 2/ is divided into a V/sub 2c/ for a cation and V/sub 2a/ for an anion. V/sub 2c/ and V/sub 2a/ may be or may be not the same value depending on electrical characteristics of the particles and the channel. It is called a cation channel if a V/sub 2c/ is much lower than a V/sub 2a/ and vice versa. It is called a cation-anion cotransporter if a V/sub 2e/ and a V/sub 2a/ are equal or almost equal. (2) Whether a particle can penetrate through a channel is mostly determined by the repulsion energies (barriers) rather than the attraction energies (wells). (3) A channel's conformation can be changed when the channel is stimulated strongly enough. The variation of the conformation could influence V/sub 2/(x) and V/sub 2/, and eventually result in open or close of the channel.