The expression of estrogen receptors in rat genioglossus muscle-derived satellite cells and its relationship to intracellular Ca2+ mobilization

Genioglossus (GG) is the most important pharyngeal dilator muscle in maintaining upper airway (UA) patency in human; therefore, its dysfunction plays an important role in pathogenesis of sleep-related breathing disorder. Recently, the expression of estrogen receptors (ERs) on mRNA and protein level has been evidenced in GG muscle; however, the cellular localization of two subtypes of ER in GG myoblasts remains unclear. The present study was designed to clarify the expression and cellular distribution of ERs in rat GG muscle-derived satellite cells (MDSCs) and further probe the effect of ERs expression on regulation of intracellular Ca2+. The immunocytochemistry revealed positive staining for both ERα and ERβ in nuclei and cytoplasm of GG MDSCs. Noticeably, positive signals for ERα and ERβ were comparable in cytoplasm, whereas the positive staining of ERα in nuclear was obviously strong than that of ERβ. More intriguingly, by using Fluo 4-AM as a fluorescent Ca2+ indicator and 17β-estradiol (E2) as a stimulant, we observed that the level of intracellular Ca2+ was not affected by E2 application, which implied that Ca2+ signaling may not be involved in ER-mediated estrogenic effects on GG MDSCs. Taken together, the present study clearly indicates the differential cellular localization of ERs in rat GG MDSCs; moreover, ER-mediated estrogenic effect in rat GG MDSCs bears no relationship to intracellular Ca2+ mobilization. In addition, the GG MDSCs express both ERα and ERβ and therefore, provide a suitable and convenient in vitro cell model for investigating the molecular mechanisms of estrogenic effects on rat GG muscle.