Protective effects of adenosine in rabbit sinoatrial node ischemia-reperfusion model in vivo: control of arrhythmia by hyperpolarization-activated cyclic nucleotide-gated (HCN)4 channels

Disturbance of cardiac rhythm is one of the consequences of myocardial ischemia/reperfusion injury. Many researchers have prompted considerable interests in developing therapeutic approaches for its control. In present study, we want to determine whether that adenosine pre- and postconditioning have protective effects on sinoatrial node ischemia/reperfusion injury on morphology, arrhythmia score, serological markers (CK-MB and cTnT), SOD activities, MDA levels and expression of HCN4 channels in SA node cells. According to the arrhythmia score recorded, whether adenosine used in terms of ischemia or reperfusion, the total number of arrhythmia was significantly reduced, as well as the number of its episodes was also markedly decreased. We have also shown a clear correlation between HCN4 channels expression and the dysfunction of SA node cells. HCN4 immunoreactivity decreased after adenosine pre- and postconditioning, but changes were significantly smaller in the cells of the SA node compared with cells of I/R group. The content of cTnT, CK-MB and MDA in adenosine pre- and postconditioning group reduced significantly; but the level of SOD increased significantly. Histological examination and electron microscopy observations found in adenosine pre- and postconditioning group sinoatrial node injury also mitigated. These findings suggested that adenosine pre- or postconditioning were to reduce the incidence of ischemia/reperfusion arrhythmias, reduce myocardial ischemia reperfusion injury. The mechanism was to stabilize the SA node cells membrane and one possible mechanism involves modulation of HCN4 channels in pacemaker cells of the sinoatrial node.