Interaction of local anesthetics with a peptide encompassing the IV/S4–S5 linker of the Na+ channel

Benzocaine complexation with p-sulfonic acid calix[n]arene: experimental ((1) H-NMR) and theoretical approaches

The aim of this work was to study the interaction between the local anesthetic benzocaine and p-sulfonic acid calix[n]arenes using NMR and theoretical calculations and to assess the effects of complexation on cytotoxicity of benzocaine. The architectures of the complexes were proposed according to (1) H NMR data (Job plot, binding constants, and ROESY) indicating details on the insertion of benzocaine in the cavity of the calix[n]arenes. The proposed inclusion compounds were optimized using the PM3 semiempirical method, and the electronic plus nuclear repulsion energy contributions were performed at the DFT level using the PBE exchange/correlation functional and the 6-311G(d) basis set. The remarkable agreement between experimental and theoretical approaches adds support to their use in the structural characterization of the inclusion complexes. In vitro cytotoxic tests showed that complexation intensifies the intrinsic toxicity of benzocaine, possibly by increasing the water solubility of the anesthetic and favoring its partitioning inside of biomembranes.

Membrane permeable local anesthetics modulate Na(V)1.5 mechanosensitivity

Voltage-gated sodium selective ion channel Na_V1.5 is expressed in the heart and the gastrointestinal tract, which are mechanically active organs. Na_V1.5 is mechanosensitive at stimuli that gate other mechanosensitive ion channels. Local anesthetic and antiarrhythmic drugs act upon Na_V1.5 to modulate activity by multiple mechanisms. This study examined whether Na_V1.5 mechanosensitivity is modulated by local anesthetics. Na_V1.5 channels wereexpressed in HEK-293 cells, and mechanosensitivity was tested in cell-attached and excised inside-out configurations. Using a novel protocol with paired voltage ladders and short pressure pulses, negative patch pressure (-30 mmHg) in both configurations produced a hyperpolarizing shift in the half-point of the voltage-dependence of activation (V_1/2a) and inactivation (V_1/2i) by about -10 mV. Lidocaine (50 µM) inhibited the pressure-induced shift of V_1/2a but not V_1/2i. Lidocaine inhibited the tonic increase in pressure-induced peak current in a use-dependence protocol, but it did not otherwise affect use-dependent block. The local anesthetic benzocaine, which does not show use-dependent block, also effectively blocked a pressure-induced shift in V_1/2a. Lidocaine inhibited mechanosensitivity in Na_V1.5 at the local anesthetic binding site mutated (F1760A). However, a membrane impermeable lidocaine analog QX-314 did not affect mechanosensitivity of F1760A Na_V1.5 when applied from either side of the membrane. These data suggest that the mechanism of lidocaine inhibition of the pressure-induced shift in the half-point of voltage-dependence of activation is separate from the mechanisms of use-dependent block. Modulation of Na_V1.5 mechanosensitivity by the membrane permeable local anesthetics may require hydrophobic access and may involve membrane-protein interactions.