Fig. 4. (A ) Dose-dependent enhancement of bupivacaine with nifedipine. Baseline tail-flick latencies were obtained before injecting 0.1 ml of vehicle or nifedipine (14.4–2,880 μm) mixed with 0.12% bupivacaine. The mice were tested for local anesthesia 30 min later. *P < 0.05 compared with the vehicle + bupivacaine control. (B ) Nifedipine increased the potency of bupivacaine. Baseline tail-flick latencies were obtained before injecting mice with 0.1 ml bupivacine mixed with vehicle (open circle, solid line) or nifedipine (28.8 μm [filled square, long-dash line], 289 μm [open triangle, dotted line], 2,888 μm [filled triangle, short-dash line]). Each dose–response curve represents 24–30 mice. %MPE = percentage of maximum possible effect.