The Role of Calcium in the Action of 5-Hydroxytryptamine and Cyclic Amp on Salivary Glands

1. The role of calcium in the potential and secretory responses of isolated salivary glands of Calliphora to 5-HT and cyclic AMP has been studied. 2. Secretion induced by 5-HT was reversibly inhibited by removal of calcium from the bathing medium. 3. The chloride-dependent depolarization of the apical membrane produced by 5-HT was calcium dependent whereas the potential response to cyclic AMP was little effected. 4. Strontium and barium effectively substituted for calcium. 5. Manganese replaced calcium at the onset of secretory and potential responses but these responses were maintained when manganese was removed. 6. Lanthanum did not substitute for calcium in secretory responses but did inhibit the secretory and potential responses to calcium in calcium-depleted glands. 7. The rate of secretion in a low-chloride medium produced by cyclic AMP was significantly lower than that induced by 5-HT, but there was little difference in normal saline. 8. A model for the mode of action of 5-HT is proposed in which calcium acts as an intracellular intermediary controlling chloride movements whilst cyclic AMP controls a potassium pump.