title: ATP evokes inward currents in corpus cavernosum myocytes.
abstract: BACKGROUND
  Although adenosine triphosphate (ATP) has often been reported to relax the corpus cavernosum, this may be mediated by indirect effects, such as release of nitric oxide from the endothelium. Recent data suggest that P2X(1) receptors may be up-regulated in diabetes, and these exert an anti-erectile effect by causing the corpus cavernosum smooth muscle cells (CCSMCs) to contract. However, to date, there is no functional evidence that ATP can directly stimulate CCSMC.
  
  
  OBJECTIVE
  This study aims to (i) to directly examine the effect of ATP on membrane currents in freshly isolated CCSMC, where influences of endothelium and other cells are absent; and (ii) to determine the receptor subtypes, ionic currents, and Ca(2+) signals stimulated by ATP.
  
  
  METHODS
  CCSMCs were enzymatically dispersed from male New Zealand White rabbits for patch clamp recording and measurement of intracellular Ca(2+) in fluo-4-loaded cells using spinning disk confocal microscopy.
  
  
  METHODS
  Patch clamp recordings were made of ATP-evoked membrane currents and spontaneous membrane currents. Spinning disk confocal imaging of intracellular Ca(2+) was performed, and the response to ATP was recorded.
  
  
  RESULTS
  ATP evoked repeatable inward currents in CCSMC (1st application: -675 ± 101 pA; 2nd application: -694 ± 120 pA, N = 9, P = 0.77). ATP-induced currents were reduced by suramin from -380 ± 121 to -124 ± 37 pA (N = 8, P < 0.05), by α,β-methylene ATP from -755 ± 235 to 139 ± 49 pA (N = 5, P < 0.05), and by NF449 from -419 ± to -51 ± 13 pA (N = 6, P < 0.05). In contrast, MRS2500, a P2Y1(1,12,13) antagonist, had no effect on ATP responses (control: -838 ± 139 pA; in MRS2500: -822 ± 184 pA, N = 13, P = 0.84) but blocked inward currents evoked by 2-MeSATP, a P2Y1,12,13 agonist (control: -623 ± 166 pA; in MRS2500: -56 ± 25 pA, N = 6, P < 0.05). The ATP-evoked inward current was unaffected by changing the transmembrane Cl(-) gradient but reversed in direction when extracellular Na(+) was reduced, indicating that it was a cation current.
  
  
  CONCLUSIONS
  ATP directly stimulates CCSMC by evoking a P2X-mediated cation current.
authors.affiliation: Smooth Muscle Research Centre, Dundalk Institute of Technology, Dundalk, Ireland.
authors.forename: Claire
authors.initials: C
authors.lastname: Doyle
authors.forename: Gerard P
authors.initials: GP
authors.lastname: Sergeant
authors.forename: Mark A
authors.initials: MA
authors.lastname: Hollywood
authors.forename: Noel G
authors.initials: NG
authors.lastname: McHale
authors.forename: Keith D
authors.initials: KD
authors.lastname: Thornbury
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D000814:Aniline Compounds / Q000032:analysis; D000818:Animals; D002118:Calcium / Q000494:pharmacology / Q000502:physiology; D008297:Male; D032342:Muscle Cells / Q000187:drug effects* / Q000502:physiology; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000502:physiology; D010410:Penile Erection / Q000187:drug effects / Q000502:physiology; D010413:Penis / Q000502:physiology*; D011817:Rabbits; D013873:Thionucleotides / Q000494:pharmacology*; D014966:Xanthenes / Q000032:analysis
chemical_list: D000814:Aniline Compounds; C409648:Fluo 4; D013873:Thionucleotides; D014966:Xanthenes; D000255:Adenosine Triphosphate; C002630:alpha,beta-methyleneadenosine 5'-triphosphate; D002118:Calcium; C008501:2-methylthio-ATP
keywords: ATP; Cation Current; Chloride Current; Corpus Cavernosum; Detumescence; Intracellular Ca2+