MMP-9 induction by 5-HT4 receptor stimulation in H4/AβPP/5-HT4 cells. A) H4/AβPP/5-HT4 cells were treated with serum-free medium, 5-HT (1 μM), or RS-67333 (3 μM) for 1, 2, 4, 8, or 24 h. Concentrated medium was analyzed in a gelatin zymography. Two bands were detected in RS-67333 treated cultures at 92 and 82 kDa corresponding to the pro and active form, respectively. B) Immunoprecipitated protein from the medium or RS-67333 (3 μM) treated for 24 h was subjected to immunoblotting using anti-MMP-9 antibody. Tubulin bands from cell lysates are also shown as an internal control.