title: Effect of tachycardia on myocardial sarcoplasmic reticulum and Ca2+ dynamics: a mechanism for preconditioning?
abstract: We have previously demonstrated that brief episodes of tachycardia prior to a prolonged occlusion of a coronary artery, followed by reperfusion, substantially reduce the infarct size. Adenosine receptors and mitochondrial ATP-dependent K(+) channels mediate this effect. Since preconditioning can be induced or reverted by maneuvers that increase or decrease [Ca(2+)](i), respectively, and tachycardia increases [Ca(2+)](i), we studied the participation of sarcoplasmic reticulum and Ca(2+) in the preconditioning effect of tachycardia. We measured the effect of ischemia and tachycardia on Ca(2+) uptake and release by sarcoplasmic reticulum vesicles isolated from left ventricular canine myocardium. Myocardial ischemia increased Ca(2+)-release rate constants and decreased both the initial rates of Ca(2+) uptake and [(3)H]-ryanodine binding by sarcoplasmic reticulum. In addition, ischemia induced a decrease in the pentameric form of phospholamban and in the content of ryanodine-receptor Ca(2+)-release channel protein. All these effects were reverted in hearts preconditioned with tachycardia. Furthermore, tachycardia by itself increased [(3)H]-ryanodine binding, Ca(2+)-release rate constants and the protein levels of ryanodine-receptor Ca(2+)-release channels and the ATP-dependent Ca(2+) pump. These results suggest that tachycardia preserves the integrity of the sarcoplasmic reticulum preventing the excess of release and the decrease of uptake of Ca(2+) produced by ischemia, thereby avoiding cytosolic Ca(2+) overload. This sarcoplasmic reticulum protection could partly explain the preconditioning effect of tachycardia.
authors.affiliation: Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Casilla 16038, Santiago 9, Chile. rdomenec@machi.med.uchile.cl
authors.forename: Raúl J
authors.initials: RJ
authors.lastname: Domenech
authors.forename: Gina
authors.initials: G
authors.lastname: Sánchez
authors.forename: Paulina
authors.initials: P
authors.lastname: Donoso
authors.forename: Víctor
authors.initials: V
authors.lastname: Parra
authors.forename: Pilar
authors.initials: P
authors.lastname: Macho
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000378:metabolism; D004285:Dogs; D006352:Heart Ventricles; D019157:Ischemic Preconditioning, Myocardial; D007700:Kinetics; D017202:Myocardial Ischemia / Q000209:etiology; D009206:Myocardium / Q000378:metabolism*; D012433:Ryanodine / Q000378:metabolism; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D013610:Tachycardia; D000099211:Phospholamban
chemical_list: D002118:Calcium; D002135:Calcium-Binding Proteins; D012433:Ryanodine; D019837:Ryanodine Receptor Calcium Release Channel; D000099211:Phospholamban