1. The role of cyclic AMP in mediating the action of 5-HT on salivary glands has been studied by measuring transepithelial potentials.

2. The lumen of unstimulated glands is 4 mV positive but becomes 12 mV negative after treatment with 5-HT (10-8M). Both the potential and the secretory responses to 5-HT are dose-dependent over the same concentration range.

3. The electrical response of salivary glands to cyclic AMP is qualitatively different to that of 5-HT; instead of going negative the potential goes more positive.

4. An increase in positive potential is also observed after treatment with theophylline (10-2M), or when glands are stimulated with 5-HT in a chloride-free saline.

5. These results are consistent with the idea that 5-HT has two actions. One is to stimulate the enzyme adenyl cyclase to synthesize cyclic AMP, which, in turn, stimulates cation transport. The other is to increase anion transport by a mechanism which is independent of cyclic AMP.

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