Effects of chloramine-T on charge movement and fraction of open channels in frog nodes of Ranvier.

The effects of chloramine-T, a substance which partially and irreversibly inhibits inactivation of the Na current (Wang 1984), on the on and off charge movement (Qon and Qoff) and on the relative position of the Qon-E and F-E curves were studied on voltage clamped frog nodes of Ranvier. The decrease of Qoff with increasing pulse duration which is seen in normal fibres was much less pronounced in chloramine-T-treated fibres, i.e. chloramine-T inhibited charge immobilization. Also, the decrease of the time constant tau off which normally accompanies the decrease of Qoff was absent in chloramine-T-treated fibres. A correlation (r2 = 0.80) between the relative tau off and the relative Qoff was observed in chloramine-T-treated fibres. The voltage dependence of the on charge movement, Qon-E, was compared with the voltage dependence of the fraction of open channels, F-E. In normal fibres, the F-E curve rose very steeply and crossed the normalized Qon-E curve so that F greater than Qon/Qon max for E greater than -40 mV. After chloramine-T treatment, the F-E curve rose less steeply and remained below the normalized Qon-E curve at all potentials. The effect of halazone was similar to that of chloramine-T but weaker. The observations about the Qon-E and F-E curve are compared with the findings on the squid giant axon.