The permeability of aconitine-modified sodium channels to univalent cations in myelinated nerve

1. 1. Ionic currents through the sodium system of nodes of Ranvier treated with aconitine were measured under voltage clamp conditions in a Ringer solution containing Na⁺ or an equimolar amount of various test cations. 2. 2. Average shifts in reversal potentials in nodes of Ranvier treated with aconitine with NH₄⁺, Li⁺, K⁺, Rb⁺, Cs⁺ in place of Na⁺ in the Ringer solution are 7.6, -6.8, -25.0, -41.0 and -51.5 mV at 13-14°C. At 20-22°C the sequence of shifts is 7.5, -5.5, -13.5, -29.0 and -41.0 mV. For Tl⁺ the average reversal potential shift is +3 mV at 20-22°C. 3. 3. The slope of the instantaneous current-voltage relation at the reversal potential in nodes treated with aconitine changed with the various cations tested. The ratios are NH₄⁺/Na⁺/K⁺/Rb⁺/Cs⁺/Li⁺ = 1.14 : 1.0 : 0.80 : 0.67 : 0.53 : 0.53. 4. 4. Using a three energy barrier model some of the parameters for the aconitine-modified Na⁺ channels were estimated (Chizmadgev, Yu. A., Khodorov, B.I. and Aityan, S.Kh. (1974) Bioelectrochem. Bioenerg. 1, 301-312).