Expression of iNOS gene in macrophages stimulated with 17β-estradiol is regulated by free intracellular Ca2+

Abstract

17β-Estradiol has potent Ca²⁺ ionophore capability and its signaling in macrophages is mediated through binding to surface and genomic receptors, resulting in transient nitric oxide (NO) elaboration. We decided to examine if the transient release of NO is due to Ca²⁺ influx pattern or the quenching effect of superoxide (^·O₂^–) through peroxynitrite formation. Differential chelation of intracellular Ca²⁺ ([Ca²⁺]i) showed that NO generation was favored by [Ca²⁺]i concentration of 237 nM. Application of an estrogen receptor antagonist ICI 182 780 resulted in attenuation of estradiol mediated NO release. Studies directed at identifying the possible role of ^·O₂^– in the attenuation of NO showed no supportive evidence. Inhibition of extracellular Ca²⁺ channel or extracellular and intracellular Ca²⁺ channels showed data consistent with a case for optimum Ca²⁺ influx signal favoring iNOS gene expression, accompanied by an elevation in iNOS protein. These data show that Ca²⁺ influx pattern determines macrophage NO elaboration.Key words: optimum Ca²⁺ signals, activation of iNOS gene, estradiol signaling.