The effect of changing the internal solution on sodium inactivation and related phenomena in giant axons.

This paper is concerned with the inactivation of the sodium system in perfused giant axons. Earlier experiments on perfused axons showed that when the artificial axoplasm was diluted with an isotonic sugar solution, action potentials could be obtained in the presence of little or no resting potential (Tasaki & Shimamura, 1962; Baker, Hodgkin & Shaw, 1962; Narahashi, 1963; Baker, Hodgkin & Meves, 1964). This is due to the fact that dilution of the internal potassium solution with a non-electrolyte causes both the inactivation curve and the relation between sodium conductance and membrane potential to shift in the direction of a more positive internal potential (Narahashi, 1963; Baker et al. 1964; Moore, Narahashi & Ulbricht, 1964). Baker et al. (1964) obtained some evidence that the shift in the inactivation, and probably the conductance, was due to the decrease in ionic strength rather than to the decrease in potassium concentration. The voltage clamp experiments presented in this paper support this conclusion. They show that the shift in the inactivation curve which occurs when the KCI is diluted with isotonic sucrose is absent when the KCI is diluted with NaCl, choline Cl or RbCl. This effect of ionic strength can be explained quantitatively by assuming a layer of fixed negative charges on the inside of the membrane. A preliminary report of some of these experiments has been given by Chandler & Meves (1964).