Fig. 5. Original penwriter records of twitch contractile force during the 10 sampling periods. Pulse trains of 100 V, 3 Hz, and 2 ms were delivered through platinum field electrodes for 5 min during each stimulation period. Note blocking effect of the two anesthetic agents. S1-S10 denote the sampling period. Bupivacaine or levobupivacaine was applied at concentrations (in μM) of 5 (S3-S4), 10 (S5-S6), 30 (S7-S8), and 100 (S9-S10).