Submitted on November 25, 2007
Accepted on March 25, 2008
Estrogen and the Ca-mobilizing Agonist ATP Evoke Acute NO Synthesis via Distinct Pathways in an Individual Human Vascular Endothelium-derived Cell
Jian-Zhong Sheng1, Furqan Arshad1, Janice E Braun2, and Andrew P Braun1*
1 Pharmacology and Therapeutics, University of Calgary, Calgary, Canada
2 Physiology and Biophysics, University of Calgary, Calgary, Canada
* To whom correspondence should be addressed. E-mail: abraun{at}ucalgary.ca.
In this study, we have systematically evaluated the signaling mechanisms underlying stimulated nitric oxide (NO) synthesis by estrogen (E2) and other vaso-active agents at the level of a single endothelium-derived cell. To do so, we have characterized and contrasted rapid E2-evoked NO synthesis with that of ATP using single cell microfluorimetry and patch clamp recordings to monitor stimulated changes in cellular NO synthesis (via DAF-FM), Ca2+ transients (via Fluo-3) and membrane hyperpolarization in cultured human EA.hy926 cells. E2-evoked NO synthesis in single cells (EC50 ~0.3 nM) was blocked by the E2 receptor antagonist ICI 182,780 and the NO synthase inhibitor L-NAME. Although both E2 and ATP stimulated comparable Ca2+ transients, E2-induced NO synthesis was insensitive to intracellular BAPTA-AM or removal of external Ca2+. In contrast, ATP-evoked NO production was abolished by either one of these treatments. ATP-evoked hyperpolarizations (~20 mV) and NO production were both inhibited by the SKCa and IKCa channel blockers apamin and charybdotoxin. E2 minimally affected membrane potential and stimulated NO synthesis was insensitive to KCa channel blockers. Exposure to either the PI-3 kinase inhibitor LY294001 or the MAP kinase inhibitor PD98059 abolished the NO response to E2, but not that to ATP. Finally, the NO response evoked by a combined stimulus of E2 + ATP was similar to that of ATP alone. In conclusion, our data directly demonstrate that an individual human EA.hy926 cell contains at least two distinct mechanisms for stimulated NO synthesis that depend upon either calcium or protein kinase signaling events.
