Potent Inactivation-Dependent Inhibition of Adult and Neonatal NaV1.5 Channels by Lidocaine and Levobupivacaine

BACKGROUND: Cardiotoxic effects of local anesthetics (LAs) involve inhibition of Na(V)1.5 voltage-gated Na+ channels. Metastatic breast and colon cancer cells also express Na(V)1.5, predominantly the neonatal splice variant (nNa(V)1.5) and their inhibition by LAs reduces invasion and migration. It may be advantageous to target cancer cells while sparing cardiac function through selective blockade of nNa(V)1.5 and/or by preferentially affecting inactivated Na(V)1.5, which predominate in cancer cells. We tested the hypotheses that lidocaine and levobupivacaine differentially affect (1) adult (aNa(V)1.5) and nNa(V)1.5 and (2) the resting and inactivated states of Na(V)1.5. METHODS: The whole-cell voltage-clamp technique was used to evaluate the actions of lidocaine and levobupivacaine on recombinant Na(V)1.5 channels expressed in HEK-293 cells. Cells were transiently transfected with cDNAs encoding either aNa(V)1.5 or nNa(V)1.5. Voltage protocols were applied to determine depolarizing potentials that either activated or inactivated 50% of maximum conductance (V 1/2 activation and V 1/2 inactivation, respectively). RESULTS: Lidocaine and levobupivacaine potently inhibited aNa(V)1.5 (IC50 mean [SD]: 20 [22] and 1 [0.6] mu M, respectively) and nNa(V)1.5 (IC50 mean [SD]: 17 [10] and 3 [1.6] mu M, respectively) at a holding potential of -80 mV. IC(50)s differed significantly between lidocaine and levobupivacaine with no influence of splice variant. Levobupivacaine induced a statistically significant depolarizing shift in the V 1/2 activation for aNa(V)1.5 (mean [SD] from -32 [4.6] mV to -26 [8.1] mV) but had no effect on the voltage dependence of activation of nNa(V)1.5. Lidocaine had no effect on V 1/2 activation of either variant but caused a significantly greater depression of maximum current mediated by nNa(V)1.5 compared to aNa(V)1.5. Similar statistically significant shifts in the V 1/2 inactivation (approximately -10 mV) occurred for both LAs and Na(V)1.5 variants. Levobupivacaine (1 mu M) caused a significantly greater slowing of recovery from inactivation of both variants than did lidocaine (10 mu M). Both LAs caused approximately 50% tonic inhibition of aNa(V)1.5 or nNa(V)1.5 when holding at -80 mV. Neither LA caused tonic block at a holding potential of either -90 or -120 mV, voltages at which there was little steady-state inactivation. Higher concentrations of either lidocaine (300 mu M) or levobupivacaine (100 mu M) caused significantly more tonic block at -120 mV. CONCLUSIONS: These data demonstrate that low concentrations of the LAs exhibit inactivation-dependent block of Na(V)1.5, which may provide a rationale for their use to safely inhibit migration and invasion by metastatic cancer cells without cardiotoxicity.