Abstract
The action of 5-hydroxytryptamine (5-HT) on an insect salivary gland was associated with a rise in adenosine-3':5'-cyclic monophosphate (cAMP) concentration and an increase in calcium uptake. An increase in secretion induced either by 5-HT or exogenous cAMP required extracellular calcium. Both 5-HT and exogenous cAMP increased (45)Ca efflux from previously labeled glands, but only 5-HT caused an increase in calcium uptake. The transepithelial potential in this tissue became more negative after addition of 5-HT, but more positive after addition of cAMP. 5-HT and cAMP induced a more negative potential when calcium was removed from the medium. It was concluded that both calcium and cAMP serve as intracellular messengers when 5-HT acts upon fly salivary gland.