Differential effects of bupivacaine enantiomers, ropivacaine and lidocaine on up-regulation of cell surface voltage-dependent sodium channels in adrenal chromaffin cells

Abstract

In cultured bovine adrenal chromaffin cells, (±)-bupivacaine inhibited veratridine-induced 22Na + influx (IC 50 6.8 μM). The IC 50 of (+)-bupivacaine (2.8 μM) was 6.2-, 7.4-, and 17.1-fold lower than those of (−)-bupivacaine (17.3 μM), (−)-ropivacaine (20.6 μM), and lidocaine (47.8 μM). Chronic (i.e. 3-h) treatment of cells with (±)-bupivacaine increased cell surface [ 3H]saxitoxin ([ 3H]STX) binding capacity by 48% (EC 50 of 233 μM; t 1/2=7.4 h), without changing the K d value. Treatment for 24 h with either (+)- or (−)-bupivacaine, or (−)-ropivacaine elevated [ 3H]STX binding, whereas 24-h treatment with lidocaine had no effect. The rise of [ 3H]STX binding by (±)-bupivacaine was prevented by cycloheximide, an inhibitor of protein synthesis, or brefeldin A, an inhibitor of cell surface vesicular exit from the trans-Golgi network; however, (±)-bupivacaine did not increase Na + channel α- and β 1-subunit mRNA levels. In cells subjected to (±)-bupivacaine treatment (1 mM for 24 h) followed by 3-h washout, veratridine-induced 22Na + influx was enhanced, even when measured in the presence of ouabain, an inhibitor of Na +,K +-ATPase. Ptychodiscus brevis toxin-3 potentiated veratridine-induced 22Na + influx by 2.3-fold in the (±)-bupivacaine-treated cells, as in non-treated cells. These results suggest that lipophilic bupivacaine enantiomers or (−)-ropivacaine acutely inhibit Na + channel gating, whereas its chronic treatment up-regulates cell surface expression of Na + channels via translational and externalization events.