Estrogen signaling at the cell surface coupled to nitric oxide release in Mytilus edulis nervous system

In previous studies we have demonstrated release of nitric oxide (NO) in human tissues following exposure to estrogen. We now designed experiments to determine whether estrogen is present in the neural tissue of Mytilus edulis, a marine mollusk, and whether, as in vertebrates, it stimulates constitutive NO synthase activity. After HPLC purification of 17β-estradiol (17β-E₂) from M. edulis ganglionic tissue, we confirmed the presence of 17β-E₂ by RIA and ES-Q-TOF-MS analysis. We further found that when either exogenous or endogenous (purified HPLC fraction) 17β-E₂ was added to pedal ganglia, there was immediate concentration-dependent NO release. Furthermore, 17β-E₂ conjugated to BSA also stimulated NO release, suggesting mediation by a membrane surface receptor. Tamoxifen, an estrogen receptor antagonist, inhibited the action of both 17β-E₂ and 17β-E₂ conjugated to BSA, further supporting the presence of an estrogen receptor. In addition, by Western blot analysis with anti-ER-β antibodies, we observed a 55-kDa protein in both the membrane and cytosolic fractions in pedal ganglia as well as in human leukocytes (that have been previously shown to express ER-β). In summary, our results suggest that a physiological dose of estrogen acutely stimulates NO release within pedal ganglia via an estrogen cell surface receptor.