| Popis: |
Simple models were examined suggesting a direct participation of Ca2+ in the mechanism of opening and closing the ionic “channels” produced by a shift of membrane potential. It is shown that these models cannot provide a simultaneous quantitative description of two interrelated phenomena; (1) dependance of the peak Na+ conductance, gNa, on potential E, and (2) the shift of the curve gNa (E) produced by the change of Ca2− concentration in the surrounding solution. Analysis suggests that the rise of conductance by depolarization is determined by displacement of some charged particles inside the membrane when a mole of particles performs the work nδEF = 3.5EF (n, the valence of hypothetical particles, δ < 1; F, the Faraday number). The physicochemical model of activation of Na+ conductance of the excitable membrane is studied. The model suggests that there are activating particles inside the membrane which make a transition under the influence of the field connected with the charge displacement. This transition produces the change of Ca2+ adsorbed by the membrane from the solution. The model explains the observed form of the curve which shows the dependence of peak Na2+ conductance on membrane potential, the magnitude of this curve shift being produced by the changes of Ca2+ in the surrounding solution and the effect of the increase of [Ca2+]0 upon the kinetic effets: the slowing down of the rise of gNa (t) produced by the depolarization and the rise or fall of gNa (t) during repolarization. |
