GPER1 and breast carcinoma: However, in addition to the binding to ERs, in human breast cancer cell lines quercetin activates signaling pathways through the G-protein-coupled receptor GPR30 (Maggiolini et al., 2004); also, in murine small intestine quercetin activates an opioid receptor (Gim et al., 2015) decreasing amplitudes and frequencies of pacemaker activity of interstitial cells of Cajal.