Bupivacaine inhibits endothelin-1-evoked increases in intracellular calcium in model sensory neurons

Background Endothelin-1 (ET-1) induces pain-like behavior in animals and man by activating the Gq protein-coupled receptor endothelin-A (ETA). Activation of ETA receptors on nociceptor membranes evokes intracellular calcium transients and alters membrane Na+ and K+ channel and TRPV1 currents, leading to neuronal hyper-excitability manifested by spontaneous and evoked pain behaviors in vivo. In addition to blocking sodium channels, local anesthetics inhibit the Gq protein-coupled signaling of several inflammatory and pro-algesic mediators. In this study, we aimed to investigate the actions of local anesthetics on ETA-mediated increases in intracellular calcium in ND7/104 model sensory neurons. Methods Increases in intracellular calcium were measured by the fluorescent indicator fura-2 in a sensory neuron-derived cell line (ND7/104), which endogenously expresses ETA receptors. Effects of lidocaine and bupivacaine, along with their respective membrane-impermeant derivatives QX-314, LEA-123 and LEA-124, on peak calcium responses to ET-1 were measured. Results Bupivacaine suppressed ET-1 responses in a concentration-dependent and non-competitive manner with an IC50 of 3.79 ± 1.63 mM. Bupivacaine (6 mM) reduced the Emax for ET-1 from 50.07 ± 1.91 mM to 27.30 ± 2.92 mM. The actions of bupivacaine occurred quickly and were rapidly reversible. Membrane-impermeant analogs of bupivacaine (LEA-123 and LEA-124, 6 mM) were without effect, as was lidocaine (10 mM) and its quaternary derivative QX-314 (10 mM). Conclusion Bupivacaine inhibits ETA-mediated calcium transients at clinically relevant concentrations through an intracellular target. The anti-inflammatory and analgesic actions of bupivacaine may be at least partially due to its inhibitory action on Gq-coupled receptors, including ETA.