Patients with temporomandibular joint disorders suffer from hyperalgesia of the masticatory muscles. Injury or inflammation result in the release of inflammatory mediators which bind to receptors such as P2X3 (homomers or heteromers) and TRPV1. Objectives: Previously collected behavioral data show that intra-masseter activation of P2X3 results in mechanical hyperalgesia which is prevented by pre-treatment of the muscle with a specific TRPV1 antagonist. This suggests P2X3 functionally interacts with TRPV1. The purpose of this experiment is to test the specificity of the drugs used in the behavioral studies. Specifically, this study was designed to confirm αβmeATP, a P2X3 agonist, directly activates P2X3, while AMG9810, a TRPV1 antagonist, directly acts on TRPV1. Methods: Ca2+ imaging was performed on dissociated trigeminal ganglia and HEK293 cells transiently transfected with TRPV1 or P2X3 cDNA. Results: αβmeATP (50μM) did not evoke a Ca2+ response in HEK293 cells transfected with TRPV1, however, the TRPV1 agonist, capsaicin (1 μM), evoked a robust Ca2+ influx. As predicted, αβmeATP (50μM) evoked Ca2+ responses in HEK293 cells expressing P2X3 and capsaicin (1 μM) did not. In the presence of the TRPV1 antagonist, AMG9810 (1 μM), αβmeATP (50μM) still evoked Ca2+ responses. However, at this time we do not have vehicle data to compare the number or amplitude of responses. Conclusions: Further studies are needed to confirm the mechanism of action of AMG9810. However, αβmeATP and capsaicin specifically activate their respective receptors. This data supports our behavioral studies which showed a functional interaction between P2X3 and TRPV1 in trigeminal sensory neurons.
Keywords: Neuroscience, Pain and TMJ and masticatory muscles