The activation of transient receptor potential vanilloid receptor subtype 1 by capsaicin without extracellular Ca2+ is involved in the mechanism of distinct substance P release in cultured rat dorsal root ganglion neurons.
Using a highly sensitive substance P (SP) radioimmunoassay, we attempted to elucidate the molecular mechanism of SP release from cultured adult rat dorsal root ganglion (DRG) neurons triggered by capsaicin. As a result, we found that capsaicin can induce SP release in the absence of extracellular Ca2+ by activating transient receptor potential vanilloid receptor subtype 1 (TRPV1). Therefore, we compared the pharmacological profile of SP release involved in several intracellular effectors (phosphoinositide 3-kinase (PI3K), Ca2+ release from intracellular stores, and mitogen-activated protein (MAP) kinases) in the presence/absence of extracellular Ca2+ by stimulating DRG neurons with various concentrations (10 to 1,000 nM) of capsaicin. In the presence of extracellular Ca2+, a capsaicin-induced maximal release of SP obtained at 100 nM capsaicin was attenuated by either the phosphoinositide 3-kinase (PI3K) inhibitors (wortmannin and LY294002), the inositol 1,4,5-triphosphate (IP3)-induced Ca2+ release blocker (2-aminoethyl diphenylborinate, 2-APB) or a specific antagonist of TRPV1 (capsazepine). In contrast, in the absence of extracellular Ca2+, only a high concentration (1 microM) of capsaicin induced a significant increase in the SP release, which was then completely abolished by either a mitogen-activated protein kinase kinase (MEK) inhibitor U0126 or capsazepine, and significantly inhibited by either thapsigargin (a Ca2+-ATPase inhibitor) or BAPTA-AM (a rapid Ca2+ chelator). In summary, the activation of TRPV1 by capsaicin modulates the SP release from DRG neurons via two different mechanisms, one requiring extracellular Ca2+, the activation of PI3K and the IP3-dependent intracellular Ca2+ release, and the other which is independent of extracellular Ca2+ but involves the activation of MEK. These data suggest that a distinct SP release mechanism exists on DRG through the activation of TRPV1 without extracellular Ca2+ by capsaicin to facilitate neuropeptide release.
Tang
He-Bin
HB
Department of Pharmacology, Graduate School of Biomedical Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima, 734-8553, Japan.
Nakata
Yoshihiro
Y
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002211:Capsaicin / Q000008:administration & dosage / Q000494:pharmacology*; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D005727:Ganglia, Spinal / Q000166:cytology / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D011863:Radioimmunoassay; D051381:Rats; D017208:Rats, Wistar; D013373:Substance P / Q000378:metabolism*; D050916:TRPV Cation Channels / Q000187:drug effects* / Q000378:metabolism
D050916:TRPV Cation Channels; C494484:TRPV1 receptor; D013373:Substance P; D015544:Inositol 1,4,5-Trisphosphate; D019869:Phosphatidylinositol 3-Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D002211:Capsaicin; D002118:Calcium