Modulation of the TRPA1 ion channel by sigma-1 receptor

Abstract

TRPA1 channels expressed in mammalian nociceptor endings play a critical role in chemonociception as a molecular sensors of reactive irritants, stress and tissue damage. Additionally, TRPA1 has been implicated in noxious cold and mechanical pain sensation. Sigma-1 receptor (σ-1R) is a chaperone mainly located in endoplasmic reticulum membrane, acting as an interoganelle signaling modulator that regulates the trafficking and function of different ionic channels. In the context of pain, pharmacological treatment of mice with the σ-1R antagonist, E-52862 (provided by ESTEVE PHARMACEUTICALS SA), produces antinociceptive effects, and has been shown to reduce the symptoms of neuropathic pain but the molecular mechanism is still unresolved. We studied the possible role of σ-1R in the modulation of TRPA1 channels and the result of this modulation on pain in mice. Measurement of intracellular calcium changes [Ca2+]i (FURA-2), and patch-clamp recordings were carried out in HEK-293 cells transfected with human TRPA1 (HEK-hTRPA1), and in cultured mouse DRG sensory neurons responsive to 50 µM AITC, a TRPA1 agonist. In both systems, incubation (4-24h) with E-52862 decreased significantly, in a dose dependent manner, the amplitude of [Ca2+]i responses evoked by AITC. Whole-cell membrane currents in HEK-hTRPA1 cells in response to AITC were also reduced, following incubation with the drug. In DRG sensory neurons the firing of action potentials, recorded in cell-attached mode, the membrane depolarization and the number of action potentials recorded in whole-cell current-clamp configuration evoked by AITC, were also significantly reduced following incubation with E-52862. In mice, we found that pain behaviors (licking, lifting and flickering) associated with TRPA1 activation by intraplantar injection of 10 mM AITC, decreased following intraperitoneal injection 24 h before of (40mg/kg) E-52862. These results implicate TRPA1 channels in the anti-nociceptive effects of σ-1R antagonists. All experimental procedures were carried out according to Spanish Royal Decree 1201/2005 and the ECC directive 2010/63/EU.