HEAT-STRESS IMPROVES FUNCTIONAL RECOVERY AND INDUCES SYNTHESIS OF 27-KDA AND 70-KDA HEAT-SHOCK PROTEINS WITHOUT PRESERVING SARCOPLASMIC-RETICULUM FUNCTION IN THE ISCHEMIC RAT-HEART

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 cellu lar organelle that plays an important role in myocardial contractility , Anesthetized rats were heat stressed for 15 min by raising temperatu re to 42 degrees C, Twenty-four hours later the hearts were perfused b y Langendorff's method and subjected to either 20 or 35 min of global ischemia, with a subset of hearts then being subjected to 19 or 20 min of reperfusion, respectively, SR function was assessed by oxalate-sup ported Ca2+ uptake rate in cell free preparations in the presence and absence of ruthenium red, a selective SR calcium release channel block er. 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 obse rved between HS v control 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 signifi cant differences seen between HS and non-HS hearts. There was signific ant improvement in developed pressure, +dP/dt and -dP/dt, with reduced creatine kinase release in HS v non-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 18 improves fu nctional recovery and induces expression of 27- and 70-kDa heat shock proteins without preservation of SR function in the globally ischemic rat heart. (C) 1996 Academic Press Limited