Figure 5. Effect of CBS inhibitor on activation and steady-state inactivation curves of sodium currents.

(A) For activation curves, the sodium currents were generated by 2 voltage pulses in 10 mV increment steps from −70 to +30 mV in a DiI-labeled DRG neuron from a rat treated with NS and a rat treated with AOAA. The reversal membrane potential (Vrev) in this recording condition was +78 mV. At different test potentials, membrane conductance (G) was measured by dividing the peak sodium current by the current driving force (Vm-Vrev) and was normalized to that recorded at +30 mV (Gmax). Data were fitted with the modified Boltzmann equation: G/Gmax = 1/{1-exp[(V-V_1/2)/k]}, where V is membrane potential, V_1/2 (V half) is the membrane voltage at which the current was half-maximally activated, and k is the slope factor. AOAA treatment did not alter the activation curve compared with NS group. There were no significant differences of V_1/2 (C) and k (D) between NS and AOAA group. (B) For steady-state inactivation curves, a conditional step of various voltages from −90 to +30 mV with 10 mV increment. These inactivation curves are representative curves of one neuron from a rat treated with NS and one neuron from a rat treated with AOAA, respectively. The peak current amplitude was normalized to that recorded at a −90 mV conditioning step (Imax). Data were plotted as a function of conditional step potentials and fitted with the negative Boltzmann equation: I/Imax = 1/{1-exp[(V_1/2-V)/k]}. AOAA treatment induced the inactivation curve rightward shift compared with the control (NS). (C) Bar graphs showed that there was no difference of V_1/2 of activation curve between NS and AOAA-treated rats. The V_1/2 of activation curve was −26.0 ± 2.9 mV (n = 10) for neurons from AOAA rats and −33.0 ± 2.5 mV (n = 8) for neurons from NS rats (p > 0.05, two sample t-test); However, AOAA treatment significantly reduced the V_1/2 of inactivation curves. The V_1/2 of inactivation curve was −33.8 ± 3.2 mV (n = 9) for neurons from NS rats and −22.7 ± 3.9 mV (n = 7) for neurons from AOAA-treated rats (*p < 0.05, two sample t-test). (D) AOAA treatment did not significantly alter the k values of activation curves and inactivation curves.