Effects of Heat Shock Protein 70 Activation by Metabolic Inhibition Preconditioning or (cid:1) -Opioid Receptor Stimulation on Ca 2 (cid:1) Homeostasis in Rat Ventricular Myocytes Subjected to Ischemic Insults

Heat shock protein 70 (HSP70) mediates delayed cardiopro- tection of preconditioning. Cytosolic calcium ([Ca 2 (cid:1) ] i ) overload precipitates injury, whereas attenuation of [Ca 2 (cid:1) ] i overload is believed to be responsible for cardioprotection. There is evi- dence suggesting a link between HSP70 and [Ca 2 (cid:1) ] i homeostasis. We hypothesize that activation of HSP70 by precondition- ing may restore [Ca 2 (cid:1) ] 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 -( (cid:1) )-3,4-dichloro- N -methyl- N -[2-(1-pyrrolidi-nyl)cyclohexyl]-benzeneacetamide (a (cid:1) -opioid receptor ago-nist)] on viability and injury, HSP70 expression, and [Ca 2 (cid:1) ] i in ventricular myocytes subjected to metabolic inhibition and an- oxia (MI/A), with blockade of HSP70 synthesis. In myocytes with vehicle pretreatment, the percentage of dead cells deter- mined by trypan blue exclusion, the injury reflected by release of lactate dehydrogenase, and the resting [Ca 2 (cid:1) ] i measured by spectrofluorometry significantly increased, whereas the ampli- tude of electrically induced [Ca 2 (cid:1) four downstream codons of rat HSP70 mRNA (Invitrogen, Carlsbad, CA) as described previously (Kim et al., 1997). Statistical Analysis. All data were expressed as means (cid:4) S.E. One-way analysis of variance followed by Newman-Keuls multiple comparison tests was carried out to test for differences between the mean values within the same study. A difference of P (cid:6) 0.05 was considered significant.