ArticleOpioid withdrawal increases transient receptor potential vanilloid 1 activity in a protein kinase A-dependent mannerSpahn, Violaa,*; Fischer, Olivera; Endres-Becker, Jeannettea; Schäfer, Michaela; Stein, Christopha; Zöllner, Christiana,bAuthor Information Sponsorships or competing interests that may be relevant to content are disclosed at the end of this article. aCharité – Universitätsmedizin Berlin, Klinik für Anaesthesiologie und operative Intensivmedizin, Campus Benjamin Franklin, Hindenburgdamm 30, Berlin 12203, Germany bUniversitätsklinikum Hamburg – Eppendorf, Klinik für Anästhesiologie, Hamburg 20251, Germany *Corresponding author. Tel.: +49 30 8445 2131; fax: +49 30 8445 4469. E-mail address:[email protected] Article history: Received 5 April 2012; Received in revised form 21 November 2012; Accepted 31 December 2012. Pain: April 2013 - Volume 154 - Issue 4 - p 598-608 doi: 10.1016/j.pain.2012.12.026 Buy Metrics Abstract Summary Opioid withdrawal-induced increased pain sensation is mediated via cAMP/protein kinase A-dependent sensitization of peripheral transient receptor potential vanilloid 1 channels. Hyperalgesia is a cardinal symptom of opioid withdrawal. The transient receptor potential vanilloid 1 (TRPV1) is a ligand-gated ion channel expressed on sensory neurons responding to noxious heat, protons, and chemical stimuli such as capsaicin. TRPV1 can be inhibited via μ-opioid receptor (MOR)-mediated reduced activity of adenylyl cyclases (ACs) and decreased cyclic adenosine monophosphate (cAMP) levels. In contrast, opioid withdrawal following chronic activation of MOR uncovers AC superactivation and subsequent increases in cAMP and protein kinase A (PKA) activity. Here we investigated (1) whether an increase in cAMP during opioid withdrawal increases the activity of TRPV1 and (2) how opioid withdrawal modulates capsaicin-induced nocifensive behavior in rats. We applied whole-cell patch clamp, microfluorimetry, cAMP assays, radioligand binding, site-directed mutagenesis, and behavioral experiments. Opioid withdrawal significantly increased cAMP levels and capsaicin-induced TRPV1 activity in both transfected human embryonic kidney 293 cells and dissociated dorsal root ganglion (DRG) neurons. Inhibition of AC and PKA, as well as mutations of the PKA phosphorylation sites threonine 144 and serine 774, prevented the enhanced TRPV1 activity. Finally, capsaicin-induced nocifensive behavior was increased during opioid withdrawal in vivo. In summary, our results demonstrate an increased activity of TRPV1 in DRG neurons as a new mechanism contributing to opioid withdrawal-induced hyperalgesia. © 2013 Lippincott Williams & Wilkins, Inc.