title: Capsaicin and N-arachidonoyl-dopamine (NADA) decrease tension by activating both cannabinoid and vanilloid receptors in fast skeletal muscle fibers of the frog.
abstract: Previous studies have indicated that vanilloid receptor (VR1) mRNA is expressed in muscle fibers. In this study, we evaluated the functional effects of VR1 activation. We measured caffeine-induced contractions in bundles of the extensor digitorum longus muscle of Rana pipiens. Isometric tension measurements showed that two VR1 agonists, capsaicin (CAP) and N-arachidonoyl-dopamine (NADA), reduced muscle peak tension to 57 ± 4 % and 71 ± 3% of control, respectively. The effect of CAP was partially blocked by a VR1 blocker, capsazepine (CPZ), but the effect of NADA was not changed by CPZ. Because NADA is able to act on cannabinoid receptors, which are also present in muscle fibers, we tested the cannabinoid antagonist AM281. We found that AM281 antagonized both CAP and NADA effects. AM281 alone reduced peak tension to 80 ± 6 % of control. With both antagonists, the CAP effect was completely blocked, and the NADA effect was partially blocked. These results provide pharmacological evidence of the functional presence of the VR1 receptor in fast skeletal muscle fibers of the frog and suggest that capsaicin and NADA reduce tension by activating both cannabinoid and vanilloid receptors.
authors.affiliation: Unidad de Investigación Dr. Enrico Stefani, Centro Universitario de Investigaciones Biomédicas de la Universidad de Colima, Av. 25 de Julio No. 965, colonia Villas de San Sebastián, CP 28040, Colima, Colima, Mexico.
authors.forename: Xóchitl
authors.initials: X
authors.lastname: Trujillo
authors.forename: Mónica
authors.initials: M
authors.lastname: Ortiz-Mesina
authors.forename: Tannia
authors.initials: T
authors.lastname: Uribe
authors.forename: Elena
authors.initials: E
authors.lastname: Castro
authors.forename: Rocío
authors.initials: R
authors.lastname: Montoya-Pérez
authors.forename: Zorayda
authors.initials: Z
authors.lastname: Urzúa
authors.forename: Alfredo
authors.initials: A
authors.lastname: Feria-Velasco
authors.forename: Miguel
authors.initials: M
authors.lastname: Huerta
mesh_terms: D000613:Aminobutyrates / Q000494:pharmacology*; D000818:Animals; D002211:Capsaicin / Q000494:pharmacology*; D018656:Muscle Fibers, Fast-Twitch / Q000187:drug effects / Q000378:metabolism*; D018657:Muscle Fibers, Slow-Twitch / Q000187:drug effects / Q000378:metabolism*; D011894:Rana pipiens; D043882:Receptors, Cannabinoid / Q000378:metabolism*; D050916:TRPV Cation Channels / Q000378:metabolism*
chemical_list: D000613:Aminobutyrates; C401954:N(gamma)-acetyl-2,4-diaminobutyric acid; D043882:Receptors, Cannabinoid; D050916:TRPV Cation Channels; C494484:TRPV1 receptor; D002211:Capsaicin