Membrane permeable local anesthetics modulate Na _V1.5 mechanosensitivity

Abstract

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.