Fig. 3. Cooling temperatures differentially affect TTXs and TTXr currents in small DRG neurons.

(A) Representative traces of TTXr (left) and TTXs (right) Na⁺ currents in DRG neurons recorded at 29, 24, 15 and 10 °C. Cells were held at −80 mV and Na⁺ channel currents were activated by 500-ms test pulses from −90 to +10 mV in steps of 10 mV. TTXr Na⁺ currents were isolated by including 500 nM TTX in the bath solution. A-803467, a Na_v 1.8 channel specific blocker (100 µM), completely blocked TTXr Na⁺ channel currents at 24 °C. (B) Summary of maximum currents (I_max, left panel) at different temperatures in TTXs (n = 10) and TTXr cells (n = 10), and percentage of maximum current at different temperatures relative to I_max at 29 °C (right panel, n = 10). (C) Voltage-dependent activation of TTXr (n = 10, left panel) and TTXs (n = 10, right panel) at 29 °C and 15 °C. Vh = −80 mV. (D) Summary of steady-state fast inactivation of TTXs (circles, n = 6) and TTXr (squares, n = 6) Na⁺ currents in DRG neurons. Experiments were performed at 29 °C (red symbols) and 10 °C (blue symbols). (E-F) Summary of steady-state slow inactivation of TTXs (D, n = 6) and TTXr (E, n = 6) Na⁺ currents in DRG neurons. Experiments were performed at 24 °C (red symbols) and 10 °C (blue symbols). Data represent Mean ± SEM. *P < 0.05, 10 °C vs. 24 °C.