Effects of GPER activation on intracellular Ca2+ stores in the vascular endothelium

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The novel G protein‐coupled estrogen receptor 1 (GPER) has been demonstrated to mediate numerous beneficial cardiovascular effects. We have begun to investigate the effects of GPER activation on intracellular Ca2+ stores in the vascular endothelium. We observed that GPER is present in primary endothelial cells in a glycosylated form. Immunostaining locates GPER at both the plasma membrane and in the perinuclear region. In nominally Ca2+‐free condition, treatment with thapsigargin triggers the release of the ER's Ca2+ content. Subsequent addition of the GPER agonist G1 in Ca2+‐free condition surprisingly triggers a slow and sustained Ca2+ rise up to ~ 400 nM, a value comparable to agonist‐induced Ca2+ entry signals. Inhibition of PI3 kinase with wortmannin decreases G1‐triggered Ca2+ signal in Ca2+ free condition, but does not abolish it, suggesting that GPER activation in endothelial cells triggers the release of both IP3‐dependent and IP3‐independent Ca2+ stores. Pretreatment of endothelial cells with brefeldin A, a disruptor of the trans‐Golgi network, abolishes the slow and prolonged phase of the Ca2+ response to G1 treatment. Our data suggest that activation of GPER in primary vascular endothelial cells triggers the release of two different types of intracellular Ca2+ stores, namely the endoplasmic reticulum and the Golgi. The data also suggest that the Golgi represents a substantial intracellular Ca2+ store in the vascular endothelium.