Abstract 5220: Cannabinoid Receptor Activation Protects Coronary Endothelium Against Reperfusion Induced Intercellular Gap Formation in a Cellular Model of Ischemia and Reperfusion
Ischemia and reperfusion provokes barrier failure of the coronary microvasculature through activation of the endothelial contractile machinery and formation of intercellular gaps, leading to myocardial edema development that jeopardizes functional recovery of the heart. In vivo studies have shown that cannabinoid receptor (CBR) activation protects reperfused hearts against reperfusion injury in terms of infarct size reduction and functional recovery. The aim of the present study is to investigate whether CBR activation with the CBR agonist R1-Methanandamide (R1M, 10 μM) can protect coronary endothelium against reperfusion induced intercellular gap formation. Cultured rat coronary endothelial monolayers were subjected to conditions of simulated ischemia (ANoxia 40min; pH6.4; no glucose) and reperfusion (NORMoxia 40min; pH7.4; with glucose). Stimulation of cannabinoid receptors during reperfusion significantly reduced reperfusion-induced intercellular gap formation (gaps[a.U.]:control:283±21; R1M:172±10*; n=12–16; *p<0.05 vs. control). CB1 receptor blocking with AM251 [250nM] during reperfusion and R1M application completely abolished the R1M mediated protection (gaps[a.U.]: R1M+AM251: 269±32#; n=10; #p<0.05 vs. R1M). Whereas the protective effect of R1M application during reperfusion could be further enhanced if AM630 [300nM], a CB2 receptor antagonist, was added to the reperfusion medium simultaneously to R1M application (gaps[a.U.]: R1M+AM630:132±23#; n=12; #p<0.05 vs. R1M). Inhibition of nitric oxide synthases (NOS) through application of L-NAME [200 μM] during reperfusion significantly blunts the protection against reperfusion induced gap formation (gaps[a.U.]:control:305±29; R1M:221±21*; R1M+L-NAME:270±27#; n=6 – 8; *p<0.05 vs. control; #p<0.05 vs. R1M). In conclusion, activation of endothelial cannabinoid receptors protects the coronary endothelium against reperfusion-induced gap formation. This protection is mediated through CB1 receptor mediated NOS activation, whereas simultaneous CB2 receptor activation diminishes this protective effect.