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CARDIOVASCULAR
-Opioid Receptor Stimulation on Ca2+ Homeostasis in Rat Ventricular Myocytes Subjected to Ischemic Insults
Department of Physiology and Institute of Cardiovascular Sciences and Medicine, The University of Hong Kong, Hong Kong Special Administrative Region, China
Heat shock protein 70 (HSP70) mediates delayed cardioprotection of preconditioning. Cytosolic calcium ([Ca2+])i overload precipitates injury, whereas attenuation of [Ca2+]i overload is believed to be responsible for cardioprotection. There is evidence suggesting a link between HSP70 and [Ca2+]i homeostasis. We hypothesize that activation of HSP70 by preconditioning may restore [Ca2+]i homeostasis altered by ischemic insults. To test the hypothesis, we determined the effects of preconditioning with metabolic inhibition or pretreating with U50,488H [trans-(+)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]-benzeneacetamide (a 
-opioid receptor agonist)] on viability and injury, HSP70 expression, and [Ca2+]i in ventricular myocytes subjected to metabolic inhibition and anoxia (MI/A), with blockade of HSP70 synthesis. In myocytes with vehicle pretreatment, the percentage of dead cells determined by trypan blue exclusion, the injury reflected by release of lactate dehydrogenase, and the resting [Ca2+]i measured by spectrofluorometry significantly increased, whereas the amplitude of electrically induced [Ca2+]i transient decreased, after 10 min with 10 mM 2-deoxy-D-glucose and 10 mM sodium dithionite, known to cause MI/A. However, when myocytes were subjected for 30 min to either 20 mM lactate and 10 mM 2-deoxy-D-glucose (MIP) or 30 µM U50,488H (UP) 20 h before MI/A, the changes in viability and injury, and [Ca2+]i responses were significantly attenuated. These were accompanied by a significantly increased HSP70 expression. Furthermore, blockade of HSP70 synthesis with selective antisense oligonucleotides abolished the beneficial effects of MIP or UP. This study provides first evidence that activation of HSP70 induced by preconditioning, which conferred delayed cardioprotection, restored partially the [Ca2+]i homeostasis altered by ischemic insults.
Address correspondence to: Prof. T. M. Wong, Department of Physiology, Faculty of Medicine, the University of Hong Kong Special Administrative Region, China. E-mail: wongtakm{at}hkucc.hku.hk
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J. Liu, K. W. L. Kam, G. H. Borchert, G. M. Kravtsov, H. J. Ballard, and T. M. Wong Further study on the role of HSP70 on Ca2+ homeostasis in rat ventricular myocytes subjected to simulated ischemia Am J Physiol Cell Physiol, February 1, 2006; 290(2): C583 - C591. [Abstract] [Full Text] [PDF]
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