title: Abundant expression and functional participation of TRPV1 at Zusanli acupoint (ST36) in mice: mechanosensitive TRPV1 as an "acupuncture-responding channel".
abstract: BACKGROUND
  Acupuncture is a therapy that involves applying mechanical stimulation to acupoints using needles. Although acupuncture is believed to trigger neural regulation by opioids or adenosine, still little is known about how physical stimulation is turned into neurological signaling. The transient receptor potential vanilloid receptors 1 and 4 (TRPV1 and TRPV4) and the acid-sensing ion channel 3 (ASIC3) are regarded as mechanosensitive channels. This study aimed to clarify their role at the Zusanli acupoint (ST36) and propose possible sensing pathways linking channel activation to neurological signaling.
  
  
  METHODS
  First, tissues from different anatomical layers of ST36 and the sham point were sampled, and channel expressions between the two points were compared using western blotting. Second, immunofluorescence was performed at ST36 to reveal distribution pattern of the channels. Third, agonist of the channels were injected into ST36 and tested in a mouse inflammatory pain model to seek if agonist injection could replicate acupuncture-like analgesic effect. Last, the components of proposed downstream sensing pathway were tested with western blotting to determine if they were expressed in tissues with positive mechanosensitive channel expression.
  
  
  RESULTS
  The results from western blotting demonstrated an abundance of TRPV1, TRPV4, and ASIC3 in anatomical layers of ST36. Furthermore, immunofluorescence showed these channels were expressed in both neural and non-neural cells at ST36. However, only capsaicin, a TRPV1 agonist, replicated the analgesic effect of acupuncture when injected into ST36. Components of calcium wave propagation (CWP, the proposed downstream sensing pathway) were also expressed in tissues with abundant TRPV1 expression, the muscle and epimysium layers.
  
  
  CONCLUSIONS
  The results demonstrated mechanosensitive channel TRPV1 is highly expressed at ST36 and possibly participated in acupuncture related analgesia. Since CWP was reported by other to occur during acupuncture and its components were shown here to express in tissues with positive TRPV1 expression. These findings suggest TRPV1 might act as acupuncture-responding channel by sensing physical stimulation from acupuncture and conducting the signaling via CWP to nerve terminals. This study provided a better understanding between physical stimulation from acupuncture to neurological signaling.
authors.forename: Shu-Yih
authors.initials: SY
authors.lastname: Wu
authors.forename: Wei-Hsin
authors.initials: WH
authors.lastname: Chen
authors.forename: Ching-Liang
authors.initials: CL
authors.lastname: Hsieh
authors.affiliation: Graduate Institute of Acupuncture Science, College of Chinese Medicine, China Medical University, 91 Hsueh-Shih Road, Taichung 40402, Taiwan. yiwenlin@mail.cmu.edu.tw.
authors.forename: Yi-Wen
authors.initials: YW
authors.lastname: Lin
mesh_terms: D062565:Acid Sensing Ion Channels / Q000378:metabolism; D015669:Acupuncture Points; D000700:Analgesics / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling; D002211:Capsaicin / Q000494:pharmacology; D040542:Mechanotransduction, Cellular; D051379:Mice; D008813:Mice, Inbred ICR; D018482:Muscle, Skeletal / Q000737:chemistry; D009412:Nerve Fibers / Q000737:chemistry; D050916:TRPV Cation Channels / Q000819:agonists / Q000378:metabolism*
chemical_list: C508378:ASIC3 protein, mouse; D062565:Acid Sensing Ion Channels; D000700:Analgesics; D050916:TRPV Cation Channels; C493921:TRPV1 protein, mouse; C486576:Trpv4 protein, mouse; D002211:Capsaicin; D002118:Calcium