The sodium channel is modeled as an aqueous cylindrical pore with inert walls except for charge rings distributed near the middle and hydrated charge blocking the inside opening. The charge rings are 2 dipoles back to back with the positive charges merged. The equations of ion diffusion through an aqueous pore with this electric field results in markedly different ion specific conductances. The ion selectivity of the charged rings can be matched quantitatively to the known relative conductances of cations in neural membranes. The mechanism of sodium conductance changes during voltage clamp experiments and in action potentials is described by nonlinear differential equations governing the interaction between sodium flux through the channel and the hydrated charge barrier. The density of hydrated charge inside the membrane is the factor controlling the opening and closing of the channel. The ion flux decreases the hydrated charge barrier which causes the positive feedback of further depolarizing sodium current. This continues until the ion flux cannot match the charge dissipation inside the membrane which results in repolarization which results in a return of the hydration barrier and a positive feedback of declining ion flux until the pore closes again. Threshold to depolarization, the time course of sodium conductance, and the refractory periods are quantitatively explained. No macromolecular rearrangements are invoked and the model is compatible with current knowledge of membrane structure.
|Original language||English (US)|
|Issue number||2 II|
|State||Published - 1975|
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