title: Spontaneous Ca2+ waves in rabbit corpus cavernosum: modulation by nitric oxide and cGMP.
abstract: BACKGROUND
  Detumescent tone and subsequent relaxation by nitric oxide (NO) are essential processes that determine the erectile state of the penis. Despite this, the mechanisms involved are incompletely understood. It is often assumed that the tone is associated with a sustained high cytosolic Ca(2+) level in the corpus cavernosum smooth muscle cells, however, an alternative possibility is that oscillatory Ca(2+) signals regulate tone, and erection occurs as a result of inhibition of Ca(2+) oscillations by NO.
  
  
  OBJECTIVE
  The aim of this study is to determine if smooth muscle cells displayed spontaneous Ca(2+) oscillations and, if so, whether these were regulated by NO.
  
  
  METHODS
  Male New Zealand white rabbits were euthanized and smooth muscle cells were isolated by enzymatic dispersal for confocal imaging of intracellular Ca(2+) (using fluo-4AM) and patch clamp recording of spontaneous membrane currents. Thin tissue slices were also loaded with fluo-4AM for live imaging of Ca(2+).
  
  
  METHODS
  Cytosolic Ca(2+) was measured in isolated smooth muscle cells and tissue slices. Results. Isolated rabbit corpus cavernosum smooth muscle cells developed spontaneous Ca(2+) waves that spread at a mean velocity of 65 microm/s. Dual voltage clamp/confocal recordings revealed that each of the Ca(2+) waves was associated with an inward current typical of the Ca(2+)-activated Cl(-) currents developed by these cells. The waves depended on an intact sarcoplasmic reticulum Ca(2+) store, as they were blocked by cyclopiazonic acid (Calbiochem, San Diego, CA, USA) and agents that interfere with ryanodine receptors and IP(3)-mediated Ca(2+) release. The waves were also inhibited by an NO donor (diethylamine NO; Tocris Bioscience, Bristol, Avon, UK), 3-(5-hydroxymethyl-2-furyl)-1-benzyl indazole (YC-1) (Alexis Biochemicals, Bingham, Notts, UK), 8-bromo-cyclic guanosine mono-phosphate (Tocris), and sildenafil (Viagra, Pfizer, Sandwich, Kent, UK). Regular Ca(2+) oscillations were also observed in whole tissue slices where they were clearly seen to precede contraction. This activity was also markedly inhibited by sildenafil, suggesting that it was under NO regulation.
  
  
  CONCLUSIONS
  These results provide a new basis for understanding detumescent tone in the corpus cavernosum and its inhibition by NO.
authors.affiliation: Smooth Muscle Research Centre, Dundalk Institute of Technology, Dundalk, Co. Louth, Ireland.
authors.forename: Gerard P
authors.initials: GP
authors.lastname: Sergeant
authors.affiliation: Biomedical Sciences, Cornell University, Ithaca, NY, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Craven
authors.affiliation: Smooth Muscle Research Centre, Dundalk Institute of Technology, Dundalk, Co. Louth, Ireland.
authors.forename: Mark A
authors.initials: MA
authors.lastname: Hollywood
authors.affiliation: Smooth Muscle Research Centre, Dundalk Institute of Technology, Dundalk, Co. Louth, Ireland.
authors.forename: Noel G
authors.initials: NG
authors.lastname: McHale
authors.affiliation: Smooth Muscle Research Centre, Dundalk Institute of Technology, Dundalk, Co. Louth, Ireland;. Electronic address: keith.thornbury@dkit.ie.
authors.forename: Keith D
authors.initials: KD
authors.lastname: Thornbury
mesh_terms: D000818:Animals; D006152:Cyclic GMP / Q000008:administration & dosage / Q000494:pharmacology*; D042541:Intracellular Space / Q000378:metabolism; D008297:Male; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects; D009569:Nitric Oxide / Q000008:administration & dosage / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D010413:Penis / Q000187:drug effects* / Q000378:metabolism*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology*; D010879:Piperazines / Q000494:pharmacology*; D011687:Purines / Q000494:pharmacology; D011817:Rabbits; D044169:Receptors, Calcium-Sensing / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D000068677:Sildenafil Citrate; D013450:Sulfones / Q000494:pharmacology*
chemical_list: D010726:Phosphodiesterase Inhibitors; D010879:Piperazines; D011687:Purines; D044169:Receptors, Calcium-Sensing; D013450:Sulfones; D009569:Nitric Oxide; D000068677:Sildenafil Citrate; D006152:Cyclic GMP