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

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 Ca 2+ 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 Ca 2+ ‐free condition, treatment with thapsigargin triggers the release of the ER's Ca 2+ content. Subsequent addition of the GPER agonist G 1 in Ca 2+ ‐free condition surprisingly triggers a slow and sustained Ca 2+ rise up to ~ 400 nM, a value comparable to agonist‐induced Ca 2+ entry signals. Inhibition of PI3 kinase with wortmannin decreases G 1 ‐triggered Ca 2+ signal in Ca 2+ free condition, but does not abolish it, suggesting that GPER activation in endothelial cells triggers the release of both IP 3 ‐dependent and IP 3 ‐independent Ca 2+ stores. Pretreatment of endothelial cells with brefeldin A, a disruptor of the trans‐Golgi network, abolishes the slow and prolonged phase of the Ca 2+ response to G 1 treatment. Our data suggest that activation of GPER in primary vascular endothelial cells triggers the release of two different types of intracellular Ca 2+ stores, namely the endoplasmic reticulum and the Golgi. The data also suggest that the Golgi represents a substantial intracellular Ca 2+ store in the vascular endothelium.