Postischemic Changes in Cardiac Sarcoplasmic Reticulum Ca 2+ Channels

Abstract

Abstract We investigated the modifications of cardiac ryanodine receptors/sarcoplasmic reticulum Ca 2+ release channels occurring in ischemic preconditioning. In an isolated rat heart model, the injury produced by 30 minutes of global ischemia was reduced by preexposure to three 3-minute periods of global ischemia (preconditioning ischemia). The protection was still present 120 minutes after preconditioning ischemia but disappeared after 240 minutes. Three 1-minute periods of global ischemia did not provide any protection. In the crude homogenate obtained from ventricular myocardium, the density of [ 3 H]ryanodine binding sites averaged 372±18 fmol/mg of protein in the control condition, decreased 5 minutes after preconditioning ischemia (290±15 fmol/mg, P <.01), was still significantly reduced after 120 minutes (298±17 fmol/mg, P <.05), and recovered after 240 minutes (341±21 fmol/mg). Three 1-minute periods of ischemia did not produce any change in ryanodine binding. The K d for ryanodine (1.5±0.3 nmol/L) was unchanged in all cases. In parallel experiments, the crude homogenate or a microsomal fraction was passively loaded with 45 Ca, and Ca 2+ -induced Ca 2+ release was studied by the quick filtration technique. In both preparations, the rate constant of Ca 2+ -induced Ca 2+ release decreased 5 and 120 minutes after preconditioning ischemia (homogenate values: 19.7±1.4 and 18.9±0.9 s −1 vs a control value of 25.4±1.7 s −1 , P <.05 in both cases) and recovered after 240 minutes (23.0±1.9 s −1 ). The Ca 2+ dependence of Ca 2+ -induced Ca 2+ release was not affected by preconditioning ischemia. In conclusion, changes in sarcoplasmic reticulum Ca 2+ -release channels occur after brief ischemia and reperfusion, are closely correlated with the development of myocardial protection versus sustained ischemia, and might play a role in the pathogenesis of ischemic preconditioning.