Alterations Of Cardiac ATP-sensitive Potassium Channel Subunits SUR2A During Cardioprotection Of Exercise Preconditioning In Rats

Objective: A short term of medium or high intensity exercise canenhance the tolerance of ischemic heart to a subsequent ischemic insult, issimilar to IP-induced cardioprotection, known as “exercise preconditioning(EP)”. The powerful cardioprotective effect of EP raise attention of sportsmedicine workers, the underlied mechanisms is the focus of currentresearch. Cardiac ATP-sensitive potassium channel (KATPchannel), a vitaleffector of EP intracellular signal transduction pathway, is involved in thepreconditioning effect of EP. Based on our previous results, the currentstudy examined the distribution of mRNA and protein of KATPchannelsubunits SUR2A, and investigated alterations of SUR2A mRNA and proteinlevels during exercise preconditioning-induced cardioprotection, thenafforded new evidences to EP-induced cardioprotection and the cellular andmolecular mechanisms of EP.Mothods:150adult (8-week-old) male Sprague-Dawley rats wererandomly assigned to6groups. Group C was control. Group EE run toexhaustion on the treadmill at30m/min, as a acute myocardial injury model.Group EEP was subjected to a high-intensity interval exercise protocol, asEP model, and rats were killed0.5h after EP. Group LEP was subjected tothe same EP protocol, and rats were killed24h after exercise. GroupEEP+EE were treated as group EEP, but run to exhaustion0.5h after EP, ratswere killed0.5h after exhaustion. Group LEP+EE were treated as groupLEP, but run to exhaustion24h after exercise, rats were killed0.5h afterexhaustion. Serum cTnI levels were measured using automatedimmunochemiluminescence and serum NT-proBNP levels were measuredusing a double-antibody sandwich enzyme-linked immunosorbent assay(ELISA). SUR2A mRNA expression were observed by in situ hybridization,real-time PCR were performed to detect the SUR2A mRNA level. Thedistribution of SUR2A protein was observed in terms ofimmunofluorescence histochemistry, SUR2A protein level was examined bywestern blotting.Results:(1) Serum cTnI and NT-proBNP levels in group EE weresignificantly higher than those in group C. No significant differences in bothof cTnI and NT-proBNP levels were found between group EEP and group C. In group LEP, serum cTnI levels had no obvious changes, but serumNT-proBNP levels were significantly lower. Serum cTnI levels andNT-proBNP levels in group EEP+EE were significantly lower than in groupEE. In group LEP+EE, serum cTnI levels in group LEP+EE weresignificantly lower, but no significant differences were found in NT-proBNPlevels.(2) SUR2A mRNA was randomly distributed throughout thecytoplasm in the form of coarse granules. Reactivity in group EE wassignificantly stronger than that in group C. Compared with group C, nosignificant differences were found in group EEP, as well as in group LEP.Reactivity in group EEP+EE was attenuated than that in group EE. Nosignificant differences were found between group LEP+EE and group EE.(3)SUR2A mRNA levels in group EE were significantly higher than those ingroup C. Compared with group C, no significant differences were found ingroup EEP, as well as in group LEP. SUR2A mRNA levels in group EEP+EEwere significantly lower than those in group EE. No significant differenceswere found between group LEP+EE and group EE.(4) Theimmunofluorescence staining of SUR2A was present in the cell membraneas well as in the striated pattern. It also demonstrated immunoreactivityalong the sarcolemma, with bright green, diffuse punctate staining of thecardiomyocyte cytoplasm. Compared with group C, immunoreactivity ingroup EE was significantly stronger, no significant differences were foundin group EEP, immunoreactivity in group EE was significantly attenuated.Immunoreactivity in group EEP+EE and group LEP+EE was significantlyattenuated than that in group EE.(5) Compared with group C, SUR2A levelsin group EE were significantly higher, no significant differences were foundin group EEP, SUR2A levels in group LEP were significantly lower. SUR2Alevels in EEP+EE and group LEP+EE were significantly lower than those ingroup EE.Conclusion: SUR2A expressed striated patterns in the cardiomyocytesand along the sarcolemma, with diffuse punctate staining of thecardiomyocyte cytoplasm. In cardioprotection against exhaustive exercisein rats induced by EP, SUR2A mRNA levels have no significant differences,SUR2A protein levels decreased significantly, suggesting that cardiac KATPchannels are involved in late cardioprotection through SUR2A proteindownregulation.