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Pregnancy-Specific Changes in VEGF Ca2+ Signaling in Uterine Artery Endothelial Cells Derek S Boeldt* , Mary A Gummer, Fu-Xian Yi, Ian M Bird Pregnancy is a time of greatly increased blood flow in the uterus to meet the needs of the growing fetus. This is achieved through the mechanisms of vasodilation and angiogenesis. In diseased states, such as preeclampsia, proper flow to the fetus is not achieved, putting both the mother and fetus at risk. We have focused on vasodilation, specifically reprogramming of cell signaling leading to production of the potent vasodilator nitric oxide (NO) in pregnancy. While it has been observed that endothelial nitric oxide synthase (eNOS) expression levels drop to equivalent levels in uterine artery endothelial cells in primary culture, derived from pregnant ewes (P-UAEC) and non-pregnant ewes (NP-UAEC) by passage 4, eNOS activity remains elevated in P-UAEC. A variety of agonists can increase eNOS activity, including ATP and VEGF, the primary agonists used in our studies. Both of these agonists are capable of causing increased Ca2+ levels in cells, presumably leading to increased eNOS activity and therefore increased NO production. The ATP induced calcium signaling mechanism has been thoroughly studied in UAEC, but much is unknown about VEGF Ca2+ signaling. Furthermore, proper function of Connexin 43 (Cx43) gap junctions is essential for maintenance of the pregnancy-specific increased sustained phase of the ATP Ca2+ response. My studies are aimed at describing the VEGF signaling mechanism in Pand NP-UAEC as it relates to Ca2+ mobilization, as well as its potential impact on ATP signaling and proper Cx43 function. Recent work has validated previous reports from the lab that the VEGF Ca2+ response is mediated by VEGFR2, and not VEGFR1 through the use of the R2 and R1 selective agonists VEGF-E and PlGF, respectively. Analysis of Ca2+ data has also revealed pregnancy related differences in not only a greater number of NP-UAEC than P-UAEC responding to VEGF-E than VEGF-165 and PlGF, but also maintaining a longer elevated Ca2+ state. This data suggests that cell-signaling events are altered in the pregnant state UAEC not only to ATP, but also VEGF, and dysfunction of these signaling changes could underlie conditions such as preeclampsia. * Supported by HD041921