Lidocaine

Lidocaine. A State Dependent Na_v Channel Inhibitor.

Voltage-gated Na⁺ channels (VGSC, Na_v) are critically important for electrogenesis and nerve impulse conduction, and as targets for important clinically relevant analgesics such as Lidocaine.
Certain Na_V channel isoforms are predominantly expressed in peripheral sensory neurons associated with pain sensation, and the expression and functional properties of Na_v channels in peripheral sensory neurons can be dynamically regulated following axonal injury or peripheral inflammation. Lidocaine is a commonly used local anesthetic as well as an antiarrhythmic drug, which is a potent and selective blocker of Na_v channels. It inhibits, for instance, human Na_v1.5 channels expressed in Xenopus oocytes in a positive rate-dependent and concentration-dependent manner, with an IC₅₀ value of 145.6 μM.
Its block can be complex, exhibiting channel state-dependent and time-dependent elements.

Reports on the effects of Lidocaine suggest that although the drug is somewhat selective in voltage-clamp experiments (the drug blocks TTX-sensitive currents at concentrations that are approximately fourfold lower than those that block high-threshold TTX-resistant currents), its functional discrimination is likely to be poor. Lidocaine block of TTX-sensitive currents indicates an IC₅₀ of between 40 and 50 μM using protocols that incorporate a negative holding potential. This block of high-threshold TTX-resistant currents has a reported IC₅₀ of about 200 μM using similar protocols.
The channel state-dependence of TTX-resistant current block has been demonstrated by a depolarization that maximally activates the current. Under these circumstances the IC₅₀ decreases to 60 μM.
Ion Channel Modulators; Voltage - Gated Na⁺ Channel Blockers.

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