Fig. 3. Morphine concentration-response relationships of acutely dissociated trigeminal ganglion neurons isolated from humanized mice expressing the μ opioid receptors 118AA (A ) or 118GG (C ) allele. Time courses of Ca²⁺current inhibition acquired during morphine (10 μM) application in a sensory neuron from 118AA (A ) and 118GG (C ) mice. The currents were evoked every 10 s by a single 70 ms test pulse to −15 mV from a holding potential of −80 mV (shown in B ). Peak current amplitudes were determined isochronally 10 ms after depolarization. The filled bars indicate application of 10 μM morphine. B  and D  show the superimposed Ca²⁺currents before (black, 1) and during (gray, 2) morphine application shown in A  and C . The concentration-response relationships of 118AA and 118GG sensory neurons exposed to morphine are illustrated in E . Each point represents the mean (± SEM) of the morphine-mediated Ca²⁺current inhibition. The numbers in parenthesis indicate the number of neurons that were tested. The smooth curves were obtained by fitting the points to the Hill equation and the IC⁵⁰(nM) values for 118AA (circles ) and 118GG (triangles ) are shown in the inset. The curve fits for each group were significantly (P < 0.0001) different from each other.