Our and in vitro studies had confirmed that mechanosensitive
ATP release and accumulation in
acupoints was elicited by acupuncture (AP), which might be a pivotal step for triggering AP
analgesia. But to date, the dynamics of extracellular
ATP (eATP) in the interstitial space during AP process was poorly known, mainly due to the low temporal resolution of the current detection approach. This study attempted to capture rapid eATP signals in vivo in the process of
needling, and further explored the role of this eATP mobilization in initiating AP
analgesic effect. Ipsilateral 20-min
needling was applied on Zusanli
acupoint (ST36) of complete
Freund's adjuvant (CFA)-induced ankle
arthritis rats. Pain thresholds were assessed in injured-side hindpaws. eATP in the interstitial space was microdialyzed and real-time quantified by
luciferin-
luciferase assay at 1-min interval with the aid of the microfluid chip. We revealed in behavioral tests that modulation of eATP levels in ST36 influenced AP
analgesic effect on ankle
arthritis. A transient eATP accumulation was induced by
needling that started to mobilize at 4 min, climbed to the peak of 11.21 nM within 3.25 min and gradually recovered. Such AP-induced eATP mobilization was significantly impacted by ankle
inflammation,
needling depth, needle manipulation, and the presence of local ecto-
nucleotidases. This work reveals that
needling elicits a transient eATP mobilization in
acupoints, which contributes to initiating AP
analgesia. This study will help us better understand the peripheral mechanism of AP
analgesia and guide clinicians to optimize the needle manipulations to improve AP efficacy.