Removal of sodium channel inactivation in squid axon by the oxidant chloramine-T.

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Abstract
The effects of a mild oxidant, chloramine-T (CT), on the Na and K currents of squid axons under voltage-clamp conditions were investigated. Sodium channel inactivation of squid gian axons was completely removed by CT at neutral pH. Internal and external CT treatment are both effective. CT apparently removes inactivation in an irreversible, all-or-none manner. The activation process of Na channel is little affected, as judged from the voltage dependence of peak Na currents, the rising phase of Na currents and the time course of tail currents following the repolarization. The removal of inactivation by CT is pH-dependent; higher pH decreases the removal rate, whereas lower pH increases it. Internal metabisulfite, a strong reductant, does not protect inactivation from the action of external CT, nor does external metabisulfite protect from internal CT application. CT slightly depresses the peak K currents at comparable concentrations but has no apparent effects on their kinetics. The neutral form of CT modified an embedded methionine residue that is involved in Na channel inactivation.