Modulation of estrogen decrease in L-pHo by specific estrogen-receptor modulators (SERMs). Experiments were done as in Fig. 4. hECE cells were grown in steroid-free medium (S.F.M.) in the absence or presence of 10 nM 17β-estradiol as well as with one of the following SERMs (all added 24 h before assays to both the luminal and contraluminal solutions): 10 μM tamoxifen (TMX), 10 μM ICI-182780 (ICI), or 1 μM progesterone (P4). Shown are means (± SD) of L-pHo determinations in three to four repeats per point. a, P < 0.01, compared with control (C), S.F.M. group; b, c, and d, P < 0.01, compared with S.F.M. group.