title: Inhibition of CaV3.2 T-type calcium channels in peripheral sensory neurons contributes to analgesic properties of epipregnanolone.
abstract: BACKGROUND
  T-type calcium channels (T-channels) play an important role in controlling excitability of nociceptors. We have previously shown that a synthetic series of 5β-reduced steroids induce a voltage-dependent blockade of T-currents in rat dorsal root ganglia (DRG) cells in vitro and induce potent analgesia to thermal stimuli in rats in vivo (Mol Pharmacol 66:1223-1235, 2004).
  
  
  OBJECTIVE
  Here, we investigated the effects of the endogenous 5β-reduced neuroactive steroid molecule, epipregnanolone [(3β,5β)-3-hydroxypregnan-20-one], on peripheral nociception.
  
  
  METHODS
  We used acutely dissociated DRG cells in vitro from adult rats as well as in vivo pain studies in mice and rats to investigate the effects of epipregnanolone on DRG T-channels.
  
  
  RESULTS
  We found that epipregnanolone reversibly blocked DRG T-currents with a half-maximal inhibitory concentration (IC50) of 2 μM and stabilized the channel in the inactive state. However, sodium, potassium, and gamma-aminobutyric acid (GABA)-gated ionic currents were not sensitive to the blocking effects of epipregnanolone even at 10 μM. In ensuing in vivo studies, we found that intraplantar (i.pl.) injections of epipregnanolone directly into peripheral receptive fields reduced responses to nociceptive heat stimuli in rats in a dose-dependent fashion. Furthermore, i.pl. epipregnanolone injections effectively reduced responses to peripheral nociceptive thermal and mechanical stimuli in wild-type mice but had no effect on the responses of CaV3.2 knockout mice.
  
  
  CONCLUSIONS
  We conclude that the inhibition of peripheral CaV3.2 T-channels contributes to the potent analgesic effect of the endogenous steroid epipregnanolone.
authors.affiliation: Department of Anesthesiology, University of Virginia Health System, Charlottesville, VA.
authors.forename: Christine
authors.initials: C
authors.lastname: Ayoola
authors.affiliation: Department of Anesthesiology, University of Virginia Health System, Charlottesville, VA.|Department of Anesthesiology and Pain Medicine, Chuncheon Sacred Heart Hospital, College of Medicine, Hallym University, Seoul, Republic of Korea.
authors.forename: Sung Mi
authors.initials: SM
authors.lastname: Hwang
authors.affiliation: Department of Anesthesiology, University of Virginia Health System, Charlottesville, VA.|Department of Anesthesiology and Pain Medicine, Kangdong Sacred Heart Hospital, College of Medicine, Hallym University Seoul, Republic of Korea.
authors.forename: Sung Jun
authors.initials: SJ
authors.lastname: Hong
authors.affiliation: Department of Anesthesiology, University of Virginia Health System, Charlottesville, VA.
authors.forename: Kirstin E
authors.initials: KE
authors.lastname: Rose
authors.affiliation: Department of Anesthesiology, University of Virginia Health System, Charlottesville, VA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Boyd
authors.affiliation: Department of Anesthesiology, University of Virginia Health System, Charlottesville, VA.
authors.forename: Neda
authors.initials: N
authors.lastname: Bozic
authors.affiliation: Department of Anesthesiology and Pain Medicine, College of Medicine, Korea University, Seoul, Republic of Korea.
authors.forename: Ji-Yong
authors.initials: JY
authors.lastname: Park
authors.affiliation: Department of Anesthesiology, University of Virginia Health System, Charlottesville, VA.
authors.forename: Hari Prasad
authors.initials: HP
authors.lastname: Osuru
authors.affiliation: Department of Anesthesiology, University of Virginia Health System, Charlottesville, VA.|Department of Neuroscience Graduate Program, University of Virginia Health System, Charlottesville, VA.
authors.forename: Michael R
authors.initials: MR
authors.lastname: DiGruccio
authors.affiliation: Department of Developmental Biology, Washington University School of Medicine, St. Louis, MO.
authors.forename: Douglas F
authors.initials: DF
authors.lastname: Covey
authors.affiliation: Department of Anesthesiology, University of Virginia Health System, Charlottesville, VA.|Department of Neuroscience, University of Virginia Health System, Charlottesville, VA.|Department of Neuroscience Graduate Program, University of Virginia Health System, Charlottesville, VA.
authors.forename: Vesna
authors.initials: V
authors.lastname: Jevtovic-Todorovic
authors.affiliation: Department of Anesthesiology, University of Virginia Health System, Charlottesville, VA.|Department of Neuroscience, University of Virginia Health System, Charlottesville, VA.|Department of Neuroscience Graduate Program, University of Virginia Health System, Charlottesville, VA.
authors.forename: Slobodan M
authors.initials: SM
authors.lastname: Todorovic
mesh_terms: D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D020747:Calcium Channels, T-Type / Q000187:drug effects* / Q000235:genetics; D005260:Female; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009619:Nociceptors / Q000187:drug effects; D010147:Pain Measurement / Q000187:drug effects; D018408:Patch-Clamp Techniques; D010525:Peripheral Nerves / Q000187:drug effects*; D011280:Pregnanolone / Q000494:pharmacology*; D051381:Rats; D011984:Sensory Receptor Cells / Q000187:drug effects*
chemical_list: D000700:Analgesics; C504883:Cacna1h protein, mouse; C509958:Cacna1h protein, rat; D002121:Calcium Channel Blockers; D020747:Calcium Channels, T-Type; D011280:Pregnanolone