The paracetamol metabolite N-acetyl-4-benzoquinoneimine (NAPQI) prevents modulation of KV7 channels via G-protein coupled receptors by interference with PIP2 and Ca2+ sensitivity

Abstract

Background and Purpose

Paracetamol has been found to alleviate inflammatory pain by modulating K_V7 channels. Its metabolite N-acetyl-4-benzoquinoneimine (NAPQI) increases currents through these channels via a stretch of three cysteine residues in the channel S2–S3 linker. Through this effect, the excitability of neurons in the pain pathway is dampened. Inflammatory mediators, in turn, enhance the excitability of sensory neurons by inhibiting K_V7 channels. Here, a specific interaction between NAPQI and the so-called inflammatory soup was investigated.

Experimental Approach

Currents through K_V7 channels were measured in sensory neurons and after heterologous expression in tsA201 cells. In addition, changes in cytosolic Ca²⁺ and in the distribution of PIP₂ (PI(4,5)P₂) between membrane and cytosol were determined by fluorescence microscopy.

Key Results

NAPQI abolished Ca²⁺-mediated inhibitory effects of an ‘inflammatory soup’ containing ADP, ATP, bradykinin, histamine, 5-hydroxytryptamine, prostaglandin E₂, substance P and a PAR2 agonist on K_V7 channel currents in sensory neurons. Moreover, the increase of K_V7.2 channel currents by quenching of cytosolic Ca²⁺ as well as the current decrease by depletion of membrane PIP₂ was impaired by NAPQI. These effects were lost in mutant channels lacking the three cysteines in the S2–S3 linker.

Conclusion and Implication

NAPQI targets the three-cysteine motif in the S2–S3 linker of K_V7.2 channels to counteract the signalling cascades employed by inflammatory mediators that inhibit these channels. In sensory neurons, this abolishes the closure of K_V7 channels by the inflammatory soup. This mechanism is likely involved in the alleviation of inflammatory pain by paracetamol.