Heat Stress Improves Functional Recovery and Induces Synthesis of 27- and 70-kDa Heat Shock Proteins Without Preserving Sarcoplasmic Reticulum Function in the Ischemic Rat Heart
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文摘
Heat stress (HS) and the subsequent expression of heat shock proteins has been shown to enhance post-ischemic functional recovery and reduce infarct size. The purpose of these experiments was to determine if HS pre-treatment preserves sarcoplasmic reticulum (SR) function, a cellular organelle that plays an important role in myocardial contractility. Anesthetized rats were heat stressed for 15 min by raising temperature to 42°C. Twenty-four hours later the hearts were perfused by Langendorff's method and subjected to either 20 or 35 min of global ischemia, with a subset of hearts then being subjected to 10 or 20 min of reperfusion, respectively. SR function was assessed by oxalate-supported Ca2+uptake rate in cell free preparations in the presence and absence of ruthenium red, a selective SR calcium release channel blocker. Ca2+uptake decreased significantly from 25.6±3.4 to 13.4±1.9 and 11.3±2.3 nmol/min/mg protein (mean±s.e.), following 20 and 35 min of ischemia, respectively. A similar trend was observed following reperfusion as well. No significant difference in Ca2+uptake was observed between HSvcontrol hearts. Similarly, in samples where the Ca2+release channel was blocked with ruthenium red, decreased Ca2+uptake rates were noted after both ischemia and reperfusion, with no significant differences seen between HS and non-HS hearts. There was significant improvement in developed pressure, +dP/dtand −dP/dt, with reduced creatine kinase release in HSvnon-HS hearts. Western blot analysis demonstrated increased synthesis of 27- and 70-kDa heat shock proteins in HS but not in control animals. It is concluded that HS improves functional recovery and induces expression of 27- and 70-kDa heat shock proteins without preservation of SR function in the globally ischemic rat heart.