Fig. 2.

Functional analysis of the NHE3 promoter by luciferase assays and identification of serotonin-responsive region. Promoter construct p-1507/+131 was transiently transfected into differentiated C2BBe1 cells (A). The effect of indicated doses of serotonin on NHE3 promoter activity was determined by luciferase assays. The luciferase activities are presented relative to the normalized activity of the promoter-less pGL2-Basic. 5′deletion NHE3 promoter constructs were transiently transfected into C2BBe1 cells and treated with or without serotonin (20 μM) for 16 h (B). Values shown are mean ± S.E. obtained from three different experiments performed in triplicate assays on different days. Statistical differences from the control values were determined by Student’s t test (‡ P = 0.007; * P = 0.006; ** P = 0.0002; *** P = 0.0001).