Local anesthetics inhibit muscarinic acetylcholine receptor-mediated calcium responses and the recruitment of β-arrestin in HSY human parotid cells

Objectives

Local anesthetics act on G protein-coupled receptors (GPCRs); thus, their potential as allosteric modulators of GPCRs has attracted attention. Intracellular signaling via GPCRs involves both G-protein- and β-arrestin-mediated pathways. To determine the effects of local anesthetics on muscarinic acetylcholine receptors (mAChR), a family of GPCRs, we analyzed the effects of local anesthetics on mAChR-mediated Ca²⁺ responses and formation of receptor–β-arrestin complexes in the HSY human parotid cell line.

Methods

Ca²⁺ responses were monitored by fura-2 spectrofluorimetry. Ligand-induced interactions between mAChR and β-arrestin were examined using a β-arrestin GPCR assay kit.

Results

Lidocaine reduced mAChR-mediated Ca²⁺ responses but did not change the intracellular Ca²⁺ concentration in non-stimulated cells. The membrane-impermeant lidocaine analog QX314 and procaine inhibited mAChR-mediated Ca²⁺ responses, with EC₅₀ values of 48.0 and 20.4 μM, respectively, for 50 μM carbachol-stimulated Ca²⁺ responses. In the absence of extracellular Ca²⁺, the pretreatment of cells with QX314 reduced carbachol-induced Ca²⁺ release, indicating that QX314 reduced Ca²⁺ release from intracellular stores. Lidocaine and QX314 did not affect store-operated Ca²⁺ entry as they did not alter the thapsigargin-induced Ca²⁺ response. QX314 and procaine reduced the carbachol-mediated recruitment of β-arrestin, and administration of procaine suppressed pilocarpine-induced salivary secretion in mice.

Conclusion

Local anesthetics, including QX314, act on mAChR to reduce carbachol-induced Ca²⁺ release from intracellular stores and the recruitment of β-arrestin. These findings support the notion that local anesthetics and their derivatives are starting points for the development of functional allosteric modulators of mAChR.