Fig. 7.

The steroids MPA, LNG, and ALDO inhibit PROG-, PGE₁-, and l-sirenin-induced calcium influx in human sperm. (A) Representative FLIPR traces showing concentration-dependent reduction of PROG-mediated increase in [Ca²⁺]_i by MPA (upper) and LNG (lower). FLIPR traces for inhibition of PGE₁- and l-sirenin-induced calcium influx by MPA and LNG are in Supplemental Figs. 7 and 8, respectively, and traces for ALDO antagonism of all three activators are in Supplemental Fig. 9. (B–E) Potencies of MPA, LNG, or ALDO for inhibiting (B) PROG-, (C) PGE₁-, (D) l-sirenin-, or (E) high K⁺/high pH-induced calcium influx. Ligand-induced activation used EC₈₀ concentrations of activator (30 nM PROG, 10 nM PGE₁, 3 µM l-sirenin). Buffer containing 140 mM K⁺, pH 8.2 was added to elicit alkalinization/depolarization calcium influx (E). The data in B–E are plotted as the mean ±SEM and expressed as a percent of the response produced by each activator alone. IC₅₀ and n values are in Table 4.