title: Amplified NO/cGMP-mediated relaxation and ryanodine receptor-to-BKCa channel signalling in corpus cavernosum smooth muscle from phospholamban knockout mice.
abstract: OBJECTIVE
  Relaxation of corpus cavernosum smooth muscle (CCSM) is induced by NO. NO promotes the formation of cGMP, which activates cGMP-dependent protein kinase I (PKGI). The large conductance calcium-activated potassium (BK(Ca) ) channel is regarded as a major target of NO/cGMP signalling; however, the mechanism of BK(Ca) activation remains unclear. The aim of the present study was to determine whether sarcoplasmic reticulum (SR) Ca(2+) load and Ca(2+) release from the SR via ryanodine receptors (RyRs) is important for BK(Ca) channel activation in response to NO/cGMP.
  
  
  METHODS
  In vitro myography was performed on CCSM strips from wild-type and PLB knockout (PLB(-/-)) mice to evaluate contraction and relaxation in response to pharmacological agents and electrical field stimulation (EFS).
  
  
  RESULTS
  In CCSM strips from PLB(-/-) mice, a model of increased SR Ca(2+) load, contractile force in response to EFS or phenylephrine (PE) was increased by nearly 100%. EFS of strips precontracted with PE induced transient relaxation in CCSM, an effect that was significantly larger in PLB(-/-) strips. Likewise, the relaxation of PE-induced contraction in response to SNP and cGMP was greater in PLB(-/-) , as demonstrated by a shift in the concentration-response curve towards lower concentrations. Blocking RyRs and BK(Ca) channels diminished the induced relaxations and eliminated the difference between wild-type and PLB(-/-).
  
  
  CONCLUSIONS
  NO/cGMP activates BK(Ca) channels through RyR-mediated Ca(2+) release. This signalling pathway is responsible for approximately 40% of the NO/cGMP effects and is amplified by increased SR Ca(2+) concentrations.
authors: Cardiovascular Medicine, Faculty of Medical and Human Sciences, University of Manchester, Manchester, UK.
authors: Shreena
authors: S
authors: Joshi
authors: Mark T
authors: MT
authors: Nelson
authors: Matthias E
authors: ME
authors: Werner
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000502:physiology; D002135:Calcium-Binding Proteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology; D006152:Cyclic GMP / Q000502:physiology*; D066298:In Vitro Techniques; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits / Q000502:physiology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D009569:Nitric Oxide / Q000502:physiology*; D010413:Penis / Q000187:drug effects / Q000502:physiology; D010656:Phenylephrine / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000502:physiology*; D012519:Sarcoplasmic Reticulum / Q000502:physiology; D015398:Signal Transduction; D000099211:Phospholamban
chemical_list: D000316:Adrenergic alpha-Agonists; D002118:Calcium; D002135:Calcium-Binding Proteins; D006152:Cyclic GMP; D051037:Large-Conductance Calcium-Activated Potassium Channel alpha Subunits; D009569:Nitric Oxide; D010656:Phenylephrine; D019837:Ryanodine Receptor Calcium Release Channel; D000099211:Phospholamban; C530995:BKCa protein, mouse