Improved adaptation to physical stress in mice overexpressing SUR2A is associated with changes in the pattern of Q-T...

The purpose of this study was to determine whether increased expression of SUR2A, a regulatory subunit of sarcolemmal ATP-sensitive K⁺ (K_ATP) channels, improves adaptation to physical stress and regulates cardiac electrophysiology in physical stress. All experiments have been done on transgenic mice in which SUR2A expression was controlled by cytomegalovirus immediate-early (CMV) promoter (SUR2A) and their littermate wild-type controls (WT). The levels of mRNA in heart tissue were measured by real-time RT-PCR. Electrocardiogram (ECG) was monitored with telemetry. The physical adaptation to stress was elucidated using treadmill. We have found that SUR2A mice express 8.34 ± 0.20 times more myocardial SUR2A mRNA than WT (n = 8-18). The tolerated workload on exercise stress test was more than twofold higher in SUR2A than in WT (n = 5-7; P = 0.01). The pattern of Q-T interval from the beginning of the exercise test until drop point was as follows in the wild type: (1) increase in Q-T interval, (2) decrease in Q-T interval, (3) steady stage with a further decrease in Q-T interval, and (4) a sharp increase in Q-T interval. The pattern of Q-T interval was different in transgenic mice and the following stages have been observed: (1) increase in Q-T interval, (2) decrease in Q-T interval, and (3) prolonged steady-state stage with a slight decrease in Q-T interval. In SUR2A mice, no stage 4 (a sharp increase in Q-T interval) was observed. Based on the obtained results, we conclude that an increase in the expression of SUR2A improves adaptation to physical stress and physical endurance by increasing the number of sarcolemmal K_ATP channels and, by virtue of their channel activity, improving Ca²⁺ homeostasis in the heart.