An approach to the physical basis of negative conductance in the squid axon.

In considering the problem of steady-state negative conductance in the squid axon from the standpoint of electrodiffusion, the following assumptions produce results which are in reasonable agreement with experimental observations: (1) The major ion distributions are not significantly perturbed by current flows (2) The electric field in the membrane is essentially uniform. (3) The membrane has certain properties appropriate to solids, particularly with respect to chemical potentials. (4) Na(+) and K(+) move according to a single-file interstitialcy migration mechanism and independently of each other. (5) The interaction energy of Na(+) with membrane sites is about 1.4 times that for K(+). Assumptions 1 and 2 are sufficient for the appearance of a negative conductance. Experimental test of the theory is possible and is specifically suggested.