Fig. 1. Effects of bupivacaine on high-voltage–activated calcium currents (HVA-Ic^a) in rat dorsal horn neurons. Neurons were clamped at −90 mV and stepped to 0 mV. (A ) HVA-Ic^ain the absence and presence of increasing concentrations of bupivacaine. (B ) Dose–response curves of bupivacaine. The abscissa scale represents the micromolar (μm) concentration of local anesthetics. The ordinate scale represents peak current in the presence of bupivacaine expressed as a percentage of the current obtained in the absence of bupivacaine. (C ) Effects of bupivacaine on the HVA-Ic^acurrent–voltage (I-V) relation. The mean peak currents are plotted as the function of testing potentials in the absence (dotted line) and presence (solid line) of 30 μm bupivacaine.