Figure 8.

Effect of MGB on I_Na(T) activated by a train of depolarizing pulses in GH₃ cells. The train was designed to consist of 40 20 ms pulses (stepped to −10 mV) separated by 5 ms intervals at −80 mV for a duration of 1 s. (A) Representative current traces taken in the control period (a, absence of MGB) and during cell exposure to 10 μM MGB. The voltage-clamp protocol is illustrated in the uppermost part. To provide a single I_Na trace, the right side of (A) denotes the expanded records from the dashed box of the left side. (B) The relationship of peak I_Na (I_Na(T)) versus the pulse train duration in the absence (filled black circles) and presence (open pink circles) of 10 μM MGB (mean ± SEM; n = 7 for each point). The continuous smooth lines over which the data points are overlaid are well-fitted by a single exponential. Of note, the presence of MGB can quicken the time course of I_Na(T) inactivation in response to a train of depolarizing pulses. (C) Summary bar graph showing the effect of MGB and MGB plus tefluthrin (Tef) on the time constant of current decay in response to a train of depolarizing command voltage from −80 to −10 mV (mean ± SEM; n = 7 for each bar). Current amplitude was measured at the beginning of each depolarizing pulse. Of note, the presence of MGB produces a significant shortening in the time constant in the decline of peak I_Na activated by a train of pulses. * Significantly different from control (p < 0.05) and ** significantly different from MGB (10 μM) alone group (p < 0.05).