Fig. 2. Inhibition of fractional ³[H]-norepinephrine release evoked with electrical stimulation.  A , In control experiments, the saline vehicle (100 μl) was added between S3 and S10.  B, C , Anesthetic agents bupivacaine (  B ) or levobupivacaine (  C ) were applied at concentrations (in μM) of 5 (S3-S4), 10 (S5-S6), 30 (S7-S8), and 100 (S9-S10).  D , Tetrodotoxin (0.1 μM), a selective inhibitor of neuronal fast Na⁺channels, was provided in periods S3-S10 for comparative purposes. Values are given as mean ± SD. *Statistical significance (  P < 0.05)  versus the saline control in the corresponding stimulation period. Six atria were tested in each group. S1-S10 denote the sampling period. Numbers below sampling period in panels  B and  C indicate the concentration of the anesthetic agent used in μM. Sal = saline; TTX = tetrodotoxin; NE = norepinephrine.