Local Anesthetics Disrupt Energetic Coupling between the Voltage-sensing Segments of a Sodium Channel

Abstract

Local anesthetics block sodium channels in a state-dependent fashion, binding with higher affi nity to open and/or inactivated states. Gating current measurements show that local anesthetics immobilize a fraction of the gating charge, suggesting that the movement of voltage sensors is modifi ed when a local anesthetic binds to the pore of the sodium channel. Here, using voltage clamp fl uorescence measurements, we provide a quantitative description of the effect of local anesthetics on the steady-state behavior of the voltage-sensing segments of a sodium channel. Lidocaine and QX-314 shifted the midpoints of the fl uorescence -voltage (F-V) curves of S4 domain III in the hyperpolarizing direction by 57 and 65 mV, respectively. A single mutation in the S6 of domain IV (F1579A), a site critical for local anesthetic block, abolished the effect of QX-314 on the voltage sensor of domain III. Both local anesthetics modestly shifted the F-V relationships of S4 domain IV toward hyperpolarized potentials. In contrast, the F-V curve of the S4 domain I was shifted by 11 mV in the depolarizing direction upon QX-314 binding. These antagonistic effects of the local anesthetic indicate that the drug modifi es the coupling between the voltage-sensing domains of the sodium channel. Our fi ndings suggest a novel role of local anesthetics in modulating the gating apparatus of the sodium channel.

Local anesthetic and antiepileptic drug access and binding to a bacterial voltage-gated sodium channel

“…4). This finding is consistent with evidence for stabilization of the depolarized up state by LAs (33,35).…”

“…At a level just below fenestrations and between S5/S6 and the VSD, BZC binds to aromatic pocket site F b , created by F107(S4), F140(S5), and F207(S6). This site may help explain block by voltage-sensor inhibition, suggested to occur close to FS6, restricting the bottom of the PD and S4-S5 linker, reducing the effect of voltage on the activation gate (15,33,34). Even more directly influencing activation, low-affinity site G b involves H-bonding to N49 and interaction via cation-π to the voltagesensing R102 (S4; see Fig.…”

“…We have also identified sites that either participate in access pathways, or may be associated with low-affinity Na v block (15), previously uncharacterized at the molecular level. These sites involve interactions between the PD and VSD, potentially affecting transmission of voltage-dependent movements to the activation gate (33).…”

Molecular basis for class Ib anti-arrhythmic inhibition of cardiac sodium channels

“…It is generally appreciated that sodium channel inhibitor action involves a number of different mechanisms 12 including pore block 13 , electrostatic interactions between the cationic charge on the drug and sodium ions at the selectivity filter 14,15 , stabilization of either fast or slow non-conducting states of the channel 16,17 , gating charge immobilization [18][19][20] , and targeted uncoupling of channel gating from voltage-sensing 21 . Previous studies have shown that site-directed mutation of two strictly conserved aromatic residues in transmembrane segment 6 (S6) of the fourth sodium channel domain (DIV), Phe1760 and Tyr1767 in Na v 1.5, can virtually abolish channel inhibition by all classes of anti-arrhythmic drugs 12,[22][23][24] .…”

Molecular motions that shape the cardiac action potential: Insights from voltage clamp fluorometry

“…VCF was first applied to skeletal muscle Na þ channels (Na V 1.4) and has been used to probe VSD interaction with inactivation (Cha et al, 1999a,b;Goldstein, 2013a, 2013b), local anesthetics (Arcisio- Miranda et al, 2010;Muroi and Chanda, 2009), and toxins (Campos et al, 2008(Campos et al, , 2007. To probe similar phenomena in the cardiac channel, we recently developed VCF protocols to track each of the VSDs of Na V 1.5.…”