Effects of aconitine and batrachotoxin on Na currents and gating currents in the frog node of Ranvier.

The effects of aconitine and batrachotoxin (BTX) on Na currents and gating currents were studied on voltage clamped frog nodes of Ranvier. The relation between steady-state values of charge movement and test pulse potential (Q-E) was compared with the fraction of open channels at a given potential (F-E). In aconitine-treated nodes the half potential, Emid, of the F-E curve was -87 mV and the slope factor, k, was 6.6 mV. Compared to normal nodes aconitine shifted the F-E curve by -53 mV along the voltage axis without significantly altering the slope. The parameters of the Qon-E curve of aconitine-treated nodes were Emid = -63 mV and k = 18.8 mV compared with Emid = -30 mV and k = 17 mV in a normal node. For the Qoff-E curve Emid was -76 mV, fairly close to Emid of the F-E curve, but the slope remained much smaller than that of the F-E curve. Thus, in aconitine-treated nodes, the normalized Qon-E and Qoff-E curves stay below the F-E curve over almost the whole potential range, a situation different from that in untreated or chloramine-T-treated nodes (Drews 1987). Similar results were obtained with BTX. The F-E curve of BTX-treated fibres had a half potential Emid = -85.1 mV and a slope factor k = 4.7 mV. In contrast to aconitine-treated nodes, the F-E curve showed a secondary rise at E greater than -50 mV.(ABSTRACT TRUNCATED AT 250 WORDS)