Involvement of K+ channel-dependant pathways in lipoxin A4-induced protective effects on hypoxia/reoxygenation injury of cardiomyocytes

Studies have shown that lipoxin A₄ (LXA₄) and activation of LXA₄ receptor provided protection against myocardial ischemia/reperfusion injury in animal models. However, the mechanisms by which LXA₄ induced protective role on myocardial ischemia/reperfusion injury remains unclear. In the present studies, we investigated the protective effects of LXA₄ on H9c2 cardiomyocytes exposed to hypoxia/reoxygenation (H/R) injury and involvement of heme oxygenase-1 (HO-1)- and K⁺ channel-dependant pathways in the LXA₄ action. H9c2 cardiomyocytes were pretreated with or without LXA₄ or HO-1 specific interfering RNA (siRNA) or various blockers and openers of K⁺ channels before exposing to H/R injury. The levels of lactate dehydrogenase (LDH) and creatine kinase (CK) in cellular supernatants and necrosis factor-α (TNF-α) in cellular lysates were measured by using ELISA. Expressions of HO-1 mRNA and protein were analyzed by using RT-PCR and Western blot respectively. Pretreatment of the cells undergoing H/R injury with LXA₄ significantly reduced the LDH and CK levels induced by H/R injury, and increased the expressions and activity of HO-1. However, the protective effects of LXA₄ were completely blocked by transfection of the cells with HO-1 siRNA, and were partially but significantly blocked by pretreatment of the cells with various blockers of K⁺ channels. The LXA₄-induced expressions of HO-1 in the cells were also inhibited by HO-1 siRNA and various blockers of K⁺ channels. The inhibitory effects of LXA₄ on enhanced TNF-α levels induced by H/R injury were abolished by transfection of the cells with HO-1 siRNA. In conclusion, the protective role of LXA₄ on cardiomyocytes against H/R injury is related to upregulation of HO-1 via reduced production of TNF-α and activation of ATP-sensitive K⁺ channels and calcium-sensitive K⁺ channel.