Figure 2 shows the current voltage (I-V) relationships of acutely dissociated TG neurons from both 118AA and 118GG mice. The Ca2+ currents were recorded employing the whole-cell variant of the patch-clamp technique and elicited with a 70 ms depolarizing step to various test pulse potentials from a holding potential of -80 mV. The current amplitude was measured isochronally 10 ms from the beginning of the test pulse. The normalized I-V curves shown in Figures 2A and 2C were recorded from 118AA (n = 36 to 58) and 118GG (n = 42 to 56) neurons, respectively. Both curves indicate that the inward current began to activate near -40 mV and reached a peak amplitude at -15 mV. Figures 2B and 2D depict superimposed Ca2+ current traces from a representative 118AA and 118GG neuron, respectively. As a result, the morphine and fentanyl concentration-response relationships described below were measured at the test potential to -15 mV from a holding potential of -80 mV. Overall, these results indicate that acutely isolated TG sensory neurons exhibited similar physical and Ca2+ channel characteristics.
