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 _V1.5 voltagegated Na ⁺ channels. Metastatic breast and colon cancer cells also express Na _V1.5, predominantly the neonatal splice variant (nNa _V1.5) 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 _V1.5 and/or by preferentially affecting inactivated Na _V1.5, which predominate in cancer cells. We tested the hypotheses that lidocaine and levobupivacaine differentially affect (1) adult (aNa _V1.5) and nNa _V1.5 and (2) the resting and inactivated states of Na _V1.5. Methods: The whole-cell voltage-clamp technique was used to evaluate the actions of lidocaine and levobupivacaine on recombinant Na _V1.5 channels expressed in HEK-293 cells. Cells were transiently transfected with cDNAs encoding either aNa _V1.5 or nNa _V1.5. Voltage protocols were applied to determine depolarizing potentials that either activated or inactivated 50% of maximum conductance (V1/2 activation and V1/2 inactivation, respectively). Results: Lidocaine and levobupivacaine potently inhibited aNa _V1.5 (IC ₅₀ mean [SD]: 20 [22] and 1 [0.6] μM, respectively) and nNa _V1.5 (IC ₅₀ mean [SD]: 17 [10] and 3 [1.6] μM, respectively) at a holding potential of -80 mV. IC ₅₀s differed significantly between lidocaine and levobupivacaine with no influence of splice variant. Levobupivacaine induced a statistically significant depolarizing shift in the V1/2 activation for aNa _V1.5 (mean [SD] from -32 [4.6] mV to -26 [8.1] mV) but had no effect on the voltage dependence of activation of nNa _V1.5. Lidocaine had no effect on V1/2 activation of either variant but caused a significantly greater depression of maximum current mediated by nNa _V1.5 compared to aNa _V1.5. Similar statistically significant shifts in the V1/2 inactivation (approximately -10 mV) occurred for both LAs and Na _V1.5 variants. Levobupivacaine (1 μM) caused a significantly greater slowing of recovery from inactivation of both variants than did lidocaine (10 μM). Both LAs caused approximately 50% tonic inhibition of aNa _V1.5 or nNa _V1.5 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 μM) or levobupivacaine (100 μM) caused significantly more tonic block at -120 mV. Conclusions: These data demonstrate that low concentrations of the LAs exhibit inactivation-dependent block of Na _V1.5, which may provide a rationale for their use to safely inhibit migration and invasion by metastatic cancer cells without cardiotoxicity.