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. 2002 Jul 1;22(13):5310–5320. doi: 10.1523/JNEUROSCI.22-13-05310.2002

Fig. 3.

Fig. 3.

Combinatorial depolarization and cAMP elevation result in a synergistic increase in VIP biosynthesis comparable to that elicited by PACAP. A, Synergistic effects of 0.5 mm isobutylmethylxanthine (IBMX), 1 mm dibutyryl cAMP (dbc), 1 mm 8-bromocyclic AMP (Brc), or 25 μm forskolin (FOR) with 40 mm KCl on induction of VIP peptide levels. The phosphodiesterase inhibitor IBMX, cAMP analogs dbc and Brc, adenylate cyclase stimulator FOR, and non-cyclase-stimulating forskolin analog 1,9-dideoxyforskolin (ddFOR; 25 μm) were applied to cultured chromaffin cells with or without 40 mm KCl, and cells and mediums were harvested 24 hr later for peptide radioimmunoassay. Experiments were performed in triplicate. *Different from KCl; p < 0.001, Scheffe's post hoc analysis. B, Dose-dependent synergistic effects of 40 mm KCl and 25 μm forskolin (FOR) on VIP peptide levels. Experiments were performed as described above, but cells and mediums were harvested for VIP peptide radioimmunoassay 72 hr after addition of drugs. Values are the mean ± SEM of triplicate or quadruplicate wells from a single cell dispersion, repeated at least once with similar results at each dosage combination. The experiment was repeated once with similar results at each dose and at least four times at concentrations of KCl, forskolin, and PACAP of 40 mm, 25 μm, and 100 nm, respectively. ∗Different from 20 mm KCl or 2.5 μm FOR, p < 0.001; #Different from 40 mm KCl or 25 μm FOR, p < 0.001; Scheffe's post hoc analysis.