Fig. 12.

DPDPE effects on secretion are mediated by a PTX-sensitive G-protein and are counteracted by Bt₂cAMP. A, The release of [³H]5-HT from GLC8 cells stimulated by either 50 mm KCl (open columns) or 1 μm thapsigargin (filled columns) is inhibited by 100 nm DPDPE in control cells as shown above (Figs. 9, 11). However, DPDPE does not inhibit the stimulated release of [³H]5-HT in cells pretreated with either PTX (100 ng/ml, overnight at 37°C) or with Bt₂cAMP (1 mm, 15 min at 37°C). B, Two concentrations of Bt₂cAMP [(1 mm(filled squares) and 10 mm(filled circles)] were tested for their ability to stimulate [³H]5-HT in the absence of other secretagogues. Whereas 1 mmBt₂cAMP is ineffective, 10 mm Bt₂cAMP stimulates a substantial release over several hours. Inset, 1 mm Bt₂cAMP (filled columns) does not synergize with either 25 mm (a, b) or 50 mm (c, d) KCl in the stimulation of [³H]5-HT release. GLC8 cells were loaded and drug-treated, and the release assayed as described in Materials and Methods. Each point in the curves and each column represent the mean ± SEM of three experiments, each performed in quadruplicate.