Brown SG, et al. – The objectives of this study are to find out if progesterone in human follicular fluid (hFF) activate CatSper and does other components of hFF modulate this effect and/or contribute separately to hFF–induced Ca2+ signaling. hFF potently stimulates CatSper and increases [Ca2+]i, primarily because of high concentrations of progesterone, however, other components of hFF also contribute to [Ca2+]i signaling, including modulation of CatSper channel activity and inhibition of [Ca2+]i oscillations.