Effects of N‐Ethylmaleimide Treatment on the Action Potential Na⁺‐Ionophore of Cultured Neuroblastoma Cells

: Treatment of murine neuroblastoma N18 cells with N‐ethylmaleimide under conditions that favor diminution of membrane potential leads to a 65% increase in the rate of veratridine‐stimulated, tetrodotoxin‐sensitive Na⁺ uptake and to a 50% decrease in the concentration of veratridine required for half‐maximal stimulation. This modification does not appear to occur in N18 cells having a normal membrane potential of approx. ‐40 mV. The data are consistent with the involvement of a sulfhydryl group in the Na⁺ channel inactivation gate and in the conformational change in this gate which results in closing of the channel.