Altered endothelial Ca2+ regulation after ischemia/reperfusion produces potentiated endothelium-derived hyperpolarizing factor-mediated dilations

Background and Purpose-Endothelium derived hyperpolarizing factor (EDHF)-mediated dilations are potentiated after several pathologies including ischemia/reperfusion (I/R) However no study to date has addressed the mechanism by which this potentiation occurs This study tested the hypothesis that potentiated EDHF mediated dilations are due to altered endothelial Ca2+ handling after I/R Methods-Rat middle cerebral arteries (MCAs) were isolated after 2 hours of MCA occlusion and 24 hours of reperfusion (or sham surgery) This model has been previously demonstrated to produce potentiated EDHF mediated dilations MCAs were studied in a pressurized/perfused vessel chamber equipped for the simultaneous measurement of endothelial Ca (+) (with fura 2) and artery diameter Measures were made after luminal administration of UTP (P2Y(2) purinoceptor agonist) 2 MeS ATP (P2Y(1) purinoceptor agonist) and Br A23187 (receptor independent Ca2+ ionophore) for sham and I/R MCAs Results-I/R resulted in significantly potentiated UTP mediated dilations (through a P2Y(2) purinoceptor) and endothelial Ca (+) responses in the presence of N-G nitro L arginine methyl ester (L NAME) and indomethacin Endothelial Ca2+ and diameter responses were also significantly potentiated with 2 MeS ATP (through a P2Y(1) purinoceptor) when L NAME and indomethacin were absent Br A23187 a receptor independent Ca2+ ionophore produced significantly potentiated endothelial Ca (+) responses after I/R in the presence of L NAME/indomethacin Evaluation of artery diameter as a function of endothelial Ca2+ demonstrated no differences between sham and I/R groups Conclustons-These findings demonstrate that I/R results in augmented endothelial Ca2+ responses that appear to be downstream of the receptor level Moreover these data suggest that this augmented Ca2+ response contributes to the potentiated EDHF mediated dilations after I/R.