Follicle-stimulating hormone and luteinizing hormone increase Ca²⁺ in the granulosa cells of mouse ovarian follicles

Abstract

In mammalian ovarian follicles, follicle stimulating hormone (FSH) and luteinizing hormone (LH) signal primarily through the G-protein G_s to elevate cAMP, but both of these hormones can also elevate Ca²⁺ under some conditions. Here we investigate FSH- and LH-induced Ca²⁺ signaling in intact follicles of mice expressing genetically encoded Ca²⁺ sensors, Twitch-2B and GCaMP6s. At a physiological concentration (1 nM), FSH elevates Ca²⁺ within the granulosa cells of preantral and antral follicles. The Ca²⁺ rise begins several minutes after FSH application, peaks at ~10 minutes, remains above baseline for another ~10 minutes, and depends on extracellular Ca²⁺. However, suppression of the FSH-induced Ca²⁺ increase by reducing extracellular Ca²⁺ does not inhibit FSH-induced phosphorylation of MAP kinase, estradiol production, or the acquisition of LH responsiveness. Like FSH, LH also increases Ca²⁺, when applied to preovulatory follicles. At a physiological concentration (10 nM), LH elicits Ca²⁺ oscillations in a subset of cells in the outer mural granulosa layer. These oscillations continue for at least 6 hours and depend on the activity of G_q family G-proteins. Suppression of the oscillations by G_q inhibition does not inhibit meiotic resumption, but does slightly attenuate ovulation. In summary, both FSH and LH increase Ca²⁺ in the granulosa cells of intact follicles, but the functions of these Ca²⁺ rises are only starting to be identified.