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

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. 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--14degrees C. At 20--22degrees C the sequence of shifts is 7.5, --5.5, --13.5, --29.0 and --41.0 mV. For Tl+ the the average reversal potential shift is +3 mV at 20--22degrees C. 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. 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).