title: Inhibition of human recombinant T-type calcium channels by N-arachidonoyl 5-HT.
abstract: OBJECTIVE
  N-arachidonoyl 5-HT (NA-5HT) has anti-nociceptive effects reported to be mediated by inhibitory actions at the transient receptor potential vanilloid receptor 1 (TRPV1) and fatty acid amide hydrolase (FAAH). Anandamide and N-arachidonoyl dopamine (NA-DA), endocannabinoids that activate TRPV1 or are metabolized by FAAH, also inhibit T-type calcium channels (I(Ca) ). T-type I(Ca) are expressed by many excitable cells, including neurons involved in pain detection and processing. We sought to determine whether NA-5HT also modulates T-type I(Ca) .
  
  
  METHODS
  Human recombinant T-type I(Ca) (Ca(V) 3 channels) expressed in HEK 293 cells were examined using standard whole-cell voltage-clamp electrophysiology techniques.
  
  
  RESULTS
  NA-5HT completely inhibited Ca(V) 3 channels with a rank order of potency (pEC(50) ) of Ca(V) 3.1 (7.4) > Ca(V) 3.3 (6.8) ≥ Ca(V) 3.2 (6.6). The effects of NA-5HT were voltage-dependent, and it produced significant hyperpolarizing shifts in Ca(V) 3 steady-state inactivation relationships. NA-5HT selectively affected Ca(V) 3.3 channel kinetics.
  
  
  CONCLUSIONS
  NA-5HT increases the steady-state inactivation of Ca(V) 3 channels, reducing the number of channels available to open during depolarization. These effects occur at NA-5HT concentrations at or below those at which NA-5HT affects TRPV1 receptors and FAAH. NA-5HT is one of the most potent inhibitors of T-type I(Ca) described to date, and it is likely to exert some of its biological effects, including anti-nociception, via inhibition of these channels.
authors.affiliation: Pain Management Research Institute, Kolling Institute, University of Sydney at Royal North Hospital St Leonards, Australia.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Gilmore
authors.forename: Marika
authors.initials: M
authors.lastname: Heblinski
authors.forename: Aaron
authors.initials: A
authors.lastname: Reynolds
authors.forename: Michael
authors.initials: M
authors.lastname: Kassiou
authors.forename: Mark
authors.initials: M
authors.lastname: Connor
mesh_terms: D000700:Analgesics / Q000494:pharmacology*; D001095:Arachidonic Acids / Q000494:pharmacology*; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D020747:Calcium Channels, T-Type / Q000502:physiology*; D057809:HEK293 Cells; D006801:Humans; D011994:Recombinant Proteins; D012701:Serotonin / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D000700:Analgesics; D001095:Arachidonic Acids; D002121:Calcium Channel Blockers; D020747:Calcium Channels, T-Type; D011994:Recombinant Proteins; C568177:arachidonyl serotonin; D012701:Serotonin