Figure 6.

Effects of luminal 5-HT on fluid secretion. The lumen of the cultured ducts was micropunctured and the luminal fluid was replaced by the HEPES-buffered solution with or without 5-HT (1 μM). The ducts were initially superfused with HEPES-buffered solution for 5 minutes. The bath solution was switched to the HCO₃^–-CO₂-buffered solution. After a 6-minute period, 1 nM secretin was added to the bath. (a) The fluid secretory rate in ducts injected with 5-HT (1 μM). Mean ± SEM of four experiments. (b) Spontaneous (HCO₃^–-CO₂–dependent) and secretin-stimulated (1 nM) fluid secretion in the absence (filled bars) and presence (open bars) of luminal 5-HT (1 μM). Mean ± SEM of four experiments.