Further Study On The Role Of HSP70 On Ca²⁺ Homeostasis In Neonatal Rat Cardiaomyoctyes Subjected To H₂O₂-induced

Heat shock protein 70(HSP70), the inducible form of a 70-KD stress protein, belongs to celluar molecular chaperones protein. HSP70 not only acts on molecular conformation and stability, but also responds to physiology process such as exciting , metabolizing , proliferation and apoptosis. But it is still unclear that how HSP70 delays impairment of cells. We hypothesized that activation of heat shock protein (HSP70) by preconditioning, which is known to confer delayed cardioprotection, attenuates the impaired handling of Ca2+ at multiple sites. To test the hypothesis, neontal rat cadiomyocytes Treat with heat shock(HS,42℃,2h) to induce the expression of HSP70,then teated with 0.5mmol/L H2O2. We first found H2O2 can reduced cadiomyocytes apoptosis and HSP70 only over-expression in the HS group, other two group only express HSP70 a little in the test of expression of HSP70.Then we tested the concentration of Ca2+ , the [Ca2+ ] of CON was 192.224+6.654(nM), the [Ca2+ ] of H2O2 group was 290.6918+8.922(nM)and the [Ca2+]of HS group was 214.2633+4.484(nM).To further determine how HSP70 repaired the Ca2+ homestasis, we measured calcium transient of each group. The calcium transient of H2O2 group had a thoroughly change : the total time was increased, the time to peak that is the time of endoplasmic reticulum (SR) releasing lots of calcium to cytosol was increased, the peak value that the most calcium concentration of was increased by 43.19% by H2O2 than those of CON group. HS group had a impaired effect on neonatal rat cardiomyocytes subjected to H2O2-induced: the total time decreased, the time to peak was decreased by 15.95% and the decay value was also decreased by HSP70 than those of H2O2 group. The results were evidence that H2O2 had an injury effect on neonatal rat myocytes, which change calcium transient that induced to calcium over-load. Heat shock can induce the the expression of HSP70 which attenuates the concentration of Ca2+ leading to delay cardioprotection. It maybe repair the ryanodine receptor (RyR) leading to releasing calcium decreasing and the Na+/Ca2+ changer (NCX) leading to calcium elimination faster.The results are evidences that activation of HSP70 by preditioning improves H2O2-imparied Ca2+ homeostasis in neonatal rat myocytes, which may be responsible , at least partly for attenuated over-load improved recovery in contractile, and cardioprotecion.