title: Role of a novel tetrodotoxin-resistant sodium channel in the nitrergic relaxation of corpus cavernosum from the South American rattlesnake Crotalus durissus terrificus.
abstract: BACKGROUND
  Coitus in snakes may last up to 28 hours; however, the mechanisms involved are unknown.
  
  
  OBJECTIVE
  To evaluate the relevance of the nitric oxide (NO)-cyclic guanosine monophosphate (cGMP)-phosphodiesterase type 5 (PDE5) system in snake corpus cavernosum reactivity.
  
  
  METHODS
  Hemipenes were removed from anesthetized South American rattlesnakes (Crotalus durissus terrificus) and studied by light and scanning electronic microscopy. Isolated Crotalus corpora cavernosa (CCC) were dissected from the non-spiny region of the hemipenises, and tissue reactivity was assessed in organ baths.
  
  
  METHODS
  Cumulative concentration-response curves were constructed for acetylcholine (ACh), sodium nitroprusside (SNP), 5-cyclopropyl-2-[1-(2-fluorobenzyl)-1H-pyrazolo[3,4-b]pyridine-3-yl]pyrimidin-4-ylamine (BAY 41-2272), and tadalafil in CCC precontracted with phenylephrine. Relaxation induced by electrical field stimulation (EFS) was also done in the absence and presence of N(ω) nitro-L-arginine methyl ester (L-NAME; 100 µM), 1H-[1, 2, 4] oxadiazolo[4,3-a]quinoxalin-1-one (ODQ; 10 µM) and tetrodotoxin (TTX; 1 µM).
  
  
  RESULTS
  The hemipenes consisted of two functionally concentric corpora cavernosa, one of them containing radiating bundles of smooth muscle fibers (confirmed by α-actin immunostaining). Endothelial and neural nitric oxide synthases were present in the endothelium and neural structures, respectively; whereas soluble guanylate cyclase and PDE5 were expressed in trabecular smooth muscle. ACh and SNP relaxed isolated CCC, with the relaxations being markedly reduced by L-NAME and ODQ, respectively. BAY 41-2272 and tadalafil caused sustained relaxations with potency (pEC(50) ) values of 5.84 ± 0.17 and 5.10 ± 0.08 (N=3-4), respectively. In precontracted CCC, EFS caused frequency-dependent relaxations that lasted three times longer than those in mammalian CC. Although these relaxations were almost abolished by either L-NAME or ODQ, they were unaffected by TTX. In contrast, EFS-induced relaxations in marmoset CC were abolished by TTX.
  
  
  CONCLUSIONS
  Rattlesnake CC relaxation is mediated by the NO-cGMP-PDE5 pathway in a manner similar to mammals. The novel TTX-resistant Na channel identified here may be responsible for the slow response of smooth muscle following nerve stimulation and could explain the extraordinary duration of snake coitus.
authors.affiliation: Department of Pharmacology, Faculty of Medical Sciences, State University of Campinas (UNICAMP), Campinas, SP, Brazil.
authors.forename: Rodrigo O
authors.initials: RO
authors.lastname: Capel
authors.forename: Fabíola Z
authors.initials: FZ
authors.lastname: Mónica
authors.forename: Marcovan
authors.initials: M
authors.lastname: Porto
authors.forename: Samuel
authors.initials: S
authors.lastname: Barillas
authors.forename: Marcelo Nicolás
authors.initials: MN
authors.lastname: Muscará
authors.forename: Simone Aparecida
authors.initials: SA
authors.lastname: Teixeira
authors.forename: André Moreira Martins
authors.initials: AM
authors.lastname: Arruda
authors.forename: Lorenzo
authors.initials: L
authors.lastname: Pissinatti
authors.forename: Alcides
authors.initials: A
authors.lastname: Pissinatti
authors.forename: André A
authors.initials: AA
authors.lastname: Schenka
authors.forename: Edson
authors.initials: E
authors.lastname: Antunes
authors.forename: César
authors.initials: C
authors.lastname: Nahoum
authors.forename: José Carlos
authors.initials: JC
authors.lastname: Cogo
authors.forename: Marco Antonio
authors.initials: MA
authors.lastname: de Oliveira
authors.forename: Gilberto
authors.initials: G
authors.lastname: De Nucci
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002144:Callithrix; D002243:Carbolines / Q000494:pharmacology; D017839:Crotalus; D006152:Cyclic GMP / Q000378:metabolism*; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5 / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000033:anatomy & histology / Q000187:drug effects; D066298:In Vitro Techniques; D008297:Male; D008855:Microscopy, Electron, Scanning; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D026602:Nitrergic Neurons / Q000187:drug effects*; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D009599:Nitroprusside / Q000494:pharmacology; D010069:Oxadiazoles / Q000494:pharmacology; D010413:Penis / Q000033:anatomy & histology / Q000098:blood supply* / Q000294:innervation*; D011720:Pyrazoles / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D026941:Sodium Channel Blockers / Q000494:pharmacology*; D015222:Sodium Channels / Q000187:drug effects* / Q000502:physiology*; D000068581:Tadalafil; D013779:Tetrodotoxin / Q000494:pharmacology*; D014665:Vasodilator Agents / Q000494:pharmacology
chemical_list: C095284:1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one; C423582:3-(4-Amino-5-cyclopropylpyrimidine-2-yl)-1-(2-fluorobenzyl)-1H-pyrazolo(3,4-b)pyridine; D002243:Carbolines; D010069:Oxadiazoles; D011720:Pyrazoles; D011725:Pyridines; D011810:Quinoxalines; D026941:Sodium Channel Blockers; D015222:Sodium Channels; D014665:Vasodilator Agents; D009599:Nitroprusside; D013779:Tetrodotoxin; D000068581:Tadalafil; D019001:Nitric Oxide Synthase; D054706:Cyclic Nucleotide Phosphodiesterases, Type 5; D006152:Cyclic GMP; D000109:Acetylcholine; D019331:NG-Nitroarginine Methyl Ester