The permeability of sodium channels to hydrogen ions in nerve fibres

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Abstract
Ionic currents in the node of Ranvier bathed in Na-free acid solutions (pH 3.4–4.6) were measured under voltage clamp conditions. Small (less than 0.1 nA) inward currents were detected in Na-free solutions at pH2+ and H+ in Na-free acid solutions showed that the inward currents in normal and aconitine-modified sodium channels were carried by hydrogen ions. Hydrogen to sodium permeability ratio was determined from reversal potential measurements. It equals to (mean ± S. E.) 252±16 and 1182±74 for normal and aconitine-modified sodium channels, respectively. The data obtained can be explained on assumption that in sodium channel energetic barriers for H+ are much lower than those for Na+. H+ however, passes through the channel very slowly because of the low rate of its removal from the acid group in selectivity filter.