Figure 4.

Kinetics of block of I_Na of Na_V1.2 by ddKIIIA or ddKIIIA[K7A], and kinetics of block of respective rI_Na's by TTX. Oocytes expressing Na_V1.2 were voltage-clamped and current recordings were obtained every 20 s as described in Materials and Methods. Example plot of peak sodium currents (I_Na) versus time during exposure to and washout of a saturating concentration (30 µM) of ddKIIIA (A) or ddKIIIA[K7A] (B). Block by ddKIIIA and ddKIIIA[K7A] leveled off at <100% (leaving rI_Na of ~5 and 25%, respectively), and washout of ddKIIIA[K7A] was faster than that of ddKIIIA. The preceding was repeated, except that after steady-state block by each peptide had been obtained, the bath was supplemented with TTX, either 100 or 10 µM with ddKIIIA (C) and ddKIIIA[K7A] (D), respectively. In each case, the rI_Na was completely blocked by TTX, albeit more slowly than when exposure was to 10 µM TTX alone (E). Following washout of both peptide and TTX, I_Na fully recovered with a time course faster than that following washout of peptide alone (compare A with C and B with D) but more slowly than that following TTX alone (compare C and D with E). For all panels, presence of TTX is indicated by an closed bar and that of peptide by a open bar. A different oocyte was used to acquire the data for each panel. Rate constants of block of rI_Na by TTX (k_obs) and recovery (k_off) for ddKIIIA and all ddKIIIA[K7X] derivatives are summarized in Table 2.