title: Anesthetic alteration of ryanodine binding by cardiac calcium release channels.
abstract: Differential cardiac contractile depression by volatile anesthetics is well documented, and evidence points to differing actions on the myocardial sarcoplasmic reticulum (SR). Since the Ca(2+)-release channel (CaRC) of the SR binds ryanodine with high-affinity when opened by micromolar Ca2+ concentrations, ryanodine binding to cardiac SR membrane vesicles was employed as an assay of anesthetic modulation of CaRC activity. Canine ventricle was homogenized, centrifuged preparatively and then differentially on a sucrose gradient. A fraction enriched with CaRCs was defined by: the presence of a approximately 450 kDa protein consistent with CaRC; approximately 3-fold enhancement of vesicular 45Ca2+ uptake by ruthenium red; Ca(2+)-activated [3H]ryanodine binding. Specific binding of 10 nM ryanodine was activated by > 0.5 microM Ca2+ and was maximal at approximately 6 pmol/mg protein in > or = 20 microM Ca2+. Halothane (1.5%), but not isoflurane, shifted the Ca(2+)-dependence of ryanodine binding to lower [Ca2+]. With submaximal activation by 5 microM Ca2+, 1.5% and 0.75% halothane enhanced binding of 10-80 microM ryanodine, while 2.5% isoflurane and 3.5% enflurane did not. A plot of bound/free vs. bound ryanodine suggests that halothane causes a dose-dependent increase in ryanodine binding to a high-affinity site, while isoflurane has no such action. In intact myocardium, this effect will decrease Ca2+ retention in the SR so that less Ca2+ will be available to activate contractions, consistent with halothane's depressant action.
authors.affiliation: Department of Anesthesiology, University of Virginia Health Sciences Center, Charlottesville 22908.
authors.forename: C
authors.initials: C
authors.lastname: Lynch
authors.forename: M J
authors.initials: MJ
authors.lastname: Frazer
mesh_terms: D000777:Anesthetics / Q000494:pharmacology*; D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects* / Q000378:metabolism; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D006352:Heart Ventricles / Q000187:drug effects* / Q000378:metabolism; D009124:Muscle Proteins / Q000187:drug effects; D012433:Ryanodine / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel; D012519:Sarcoplasmic Reticulum / Q000187:drug effects
chemical_list: D000777:Anesthetics; D015220:Calcium Channels; D009124:Muscle Proteins; D019837:Ryanodine Receptor Calcium Release Channel; D012433:Ryanodine; D002118:Calcium