Altered endothelial Ca2+ regulation after ischemia/reperfusion produces potentiated endothelium-derived hyperpolarizing factor-mediated dilations.
OBJECTIVE
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 Ca2+ (with fura 2) and artery diameter. Measures were made after luminal administration of UTP (P2Y2 purinoceptor agonist), 2 MeS-ATP (P2Y1 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 P2Y2 purinoceptor) and endothelial Ca2+ 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 P2Y1 purinoceptor) when L-NAME and indomethacin were absent. Br-A23187, a receptor-independent Ca2+ ionophore, produced significantly potentiated endothelial Ca2+ 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.


CONCLUSIONS
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.
Marrelli
Sean P
SP
Department of Anesthesiology, Baylor College of Medicine, Houston, Tex 77030, USA. marrelli@bcm.tmc.edu
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D001685:Biological Factors / Q000378:metabolism* / Q000494:pharmacology; D002545:Brain Ischemia / Q000209:etiology / Q000503:physiopathology*; D002118:Calcium / Q000378:metabolism*; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000187:drug effects / Q000503:physiopathology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005456:Fluorescent Dyes; D066298:In Vitro Techniques; D020244:Infarction, Middle Cerebral Artery / Q000150:complications; D007476:Ionophores / Q000494:pharmacology; D008297:Male; D020768:Middle Cerebral Artery / Q000187:drug effects / Q000503:physiopathology; D051381:Rats; D020318:Rats, Long-Evans; D018048:Receptors, Purinergic P2 / Q000378:metabolism; D058472:Receptors, Purinergic P2Y1; D058473:Receptors, Purinergic P2Y2; D015424:Reperfusion; D013873:Thionucleotides / Q000494:pharmacology; D014544:Uridine Triphosphate / Q000494:pharmacology; D014654:Vascular Patency / Q000187:drug effects; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*
D001685:Biological Factors; D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D007476:Ionophores; C546384:P2ry1 protein, rat; C546387:P2ry2 protein, rat; D018048:Receptors, Purinergic P2; D058472:Receptors, Purinergic P2Y1; D058473:Receptors, Purinergic P2Y2; D013873:Thionucleotides; C067410:endothelium-dependent hyperpolarization factor; D000255:Adenosine Triphosphate; D002118:Calcium; D014544:Uridine Triphosphate; C008501:2-methylthio-ATP