title: Diketopyridylryanodine has three concentration-dependent effects on the cardiac calcium-release channel/ryanodine receptor.
abstract: By interacting with more than one site, ryanoids induce multiple effects on calcium-release channels. To date, the kinetics of interaction of only one of these sites has been characterized. Using C(4),C(12)-diketopyridylryanodine in both [(3)H]ryanodine binding and single channel experiments we characterized another site on the cardiac ryanodine receptor (RyR2) with which ryanoids interact. Competitive binding of this ryanoid to RyR2 implied a minimal two-site binding model. At the single channel level, C(4),C(12)-diketopyridylryanodine induced three distinct effects. At nanomolar concentrations, it increased channel open probability severalfold without inducing a subconductance. This effect was independent of membrane holding potential. As for other ryanoids, low micromolar concentrations of C(4),C(12)-diketopyridylryanodine readily induced a subconductance state. The major subconductance had a current amplitude of 52% of fully open, it was reversible, and its time to induction and duration were voltage- and concentration-dependent, affording Hill slopes of >2. At higher micromolar concentrations C(4),C(12)-diketopyridylryanodine induced long lasting, yet reversible shut states. Using a pharmacological strategy we have discerned an additional ryanoid-binding site on RyR2 that triggers an increase in channel activity. This site likely resides outside the strict confines of the transmembrane conducting pathway.
authors.affiliation: Department of Pharmacology, University of Nebraska Medical Center, Omaha 68198, USA. kbidasee@unmc.edu
authors.forename: Keshore R
authors.initials: KR
authors.lastname: Bidasee
authors.forename: Le
authors.initials: L
authors.lastname: Xu
authors.forename: Gerhard
authors.initials: G
authors.lastname: Meissner
authors.forename: Henry R
authors.initials: HR
authors.lastname: Besch
mesh_terms: D000465:Algorithms; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D020128:Inhibitory Concentration 50; D007700:Kinetics; D008024:Ligands; D008956:Models, Chemical; D008958:Models, Molecular; D009206:Myocardium / Q000378:metabolism*; D011485:Protein Binding; D012433:Ryanodine / Q000031:analogs & derivatives / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D013997:Time Factors
chemical_list: C474026:C4,C12-diketopyridylryanodine; D008024:Ligands; D019837:Ryanodine Receptor Calcium Release Channel; D012433:Ryanodine; D002118:Calcium