| Objective:To investigate effects of upregulation expression of myocardium heat shock protein 70 due to heat stress on electrical remodeling and expression of the Cav1.2,α1c,Kca 3.1mRNA and protein induced by rapid atrial pacing in in rabbits. Methods:Thirty-two healthy adult New Zealand rabbits were randomly divided into heat stress groups (n=8), Pacing groups (n=8),atorvastatin groups(n=8) and sham groups (n=8). Heat stress is that New Zealand rabbits were administered ketamine with intraperitoneal in 30mg/kg, muscles injection, then placed them into the heated incubator, used ice packs to protect their heads, measured the cylinder temperatures to 41℃, continued for 15 minuets, then placed them in room temperature for 24h. Atorvastatin pretreatment group was given atorvastatin by 2.0mg-Kg-1·-d-1by gavage one week before pacing.After rapid right atrial pacing at 600 bpm 6h, the parameters reflecting the change of atrial electrophysiology properties were measurred, during AERP, adaptation of AERP, the inducibility of atrial fibrillation at 0h,2h,4h,6h. sham groups received electrophysiological testing only without pacing. HSP70mRNA,HSP70, LVDCCα1c, mRNA, LVDCCalc protein, KCa3.1 mRNA and Kca3.1protein of the myocardial content was detected by RT-PCR. Results:(1) after pacing, AERP200 and AERP150 were immediately shortened AERP200 (79.38±6.23) ms, AERP,150 (71.25±6.94) ms, P< 0.01]; but there were no significant changes in heat stress group, atorvastatin group and the sham group before and after pacing. (2) Before rapid atrial pacing, at RA in pacing group was (AERP2oo-AERP150)/50ms 0.21±0.10, and it was 0.16±0.07,0.14±0.05,0.13±0.05, P<0.01, after pacing for 2h,4h,6h, this showed that tips AERP rate adaptation decreased gradually; there was no significant difference in other groups before and after pacing. (3) the inducibility of atrial fibrillation in each group were by programmed and burst stimulation.The the inducibility of atrial fibrillation of sham groups were 25% at each time point;The the inducibility of atrial fibrillation of pacing groups respectively were 37.5%,75%,100%,100%at pacing 0h,2h,4h,6h.Them were respective 25%,37.5%,37.5%,50% in heat stress groups;Them were respective 37.5%,50%,50%,62.5% inatorvastatin group, It did not significant change during the 6h of pacing in sham groups. (4)The expression of HSP70 and HSP70mRNA of all parts of the heart in Heat stress group and the atorvastatin group was significantly higher (P< 0;05). There was no significant changes between pacing group and the sham group. The expression of Cav1.2,α1c,mRNA,Cav1.2,α1c and Kca3.1mRNA,Kca3.1 protein in pacing group was decreased compared with heat stress group and the sham group.But it had no statistical difference among heat stress group, A asked atorvastatin group and the sham group. Conclusions:(1) heat stress to rabbit maintain rectal temperature at 41℃for 15min induced upregulation of atrial expression of HSP70, high expression of HSP70 was able to reduce of inducement of atrial electrical remodeling and AF by atrial pacing significantly; (2) Atorvastatin increased the expression of HSP70mRNA in myocardial, and it had significant preventive role to myocardial electrical remodeling and AF induced by atrial pacing; (3) the Expression of HSP70 is an important factor which can influence atrial ER and AF; (4) the upregulation of HSP70 in Myocardial inhibited rapid atrial pacing induced reconstruction of Cav1.2,α1c and Kca3.1; (5) Atorvastatin suppressed rapid atrial pacing inducd Reconstruction of Cav1.2,α1c and Kca3.1 via increasing HSP70 expression; (6) Preventative effect of HSP70 high expression to atrial ER and AF maintained 6 h.
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