Quantitative description of the sodium conductance of the giant axon of Myxicola in terms of a generalized second-order variable.

A variety of experimental observations in Myxicola and other preparations indicate that the sodium conductance, gNa, has properties quite different from those described by the m and h variables of Hodgkin and Huxley. A new quantitative description of the gNa is presented in which the gNa is assumed to be proportional to the fifth power of a generalized second-order variable, i.e., gNa = g'Na times v to the fifth, v = -Kav + K2U = K3, U = K4U + K5v + K6. This model is shown to be able to quantitatively simulate all of the experimentally observed behavior of the gNa. A view of the sodium gate consistent with these kinetics is to imagine it to be composed of five independent subunits, each of the type A eq. B eq. C eq. A where A represents the resting state, B the conducting state, and C the inactivated state. A model in which the subunit is of the type A eq. B eq. C could not simulate the experimental observations. It was concluded that two processes are sufficient to account for all of the behavior of the gNa.