EFFECTS OF 2 NEURONAL ANTIDIURETIC MOLECULES, NEUROPARSIN AND 5-HYDROXYTRYPTAMINE, ON CYTOSOLIC-FREE CALCIUM MONITORED WITH INDO-1 IN EPITHELIAL AND MUSCULAR CELLS OF THE AFRICAN LOCUST RECTUM

Using the probe indo-1 in a microspectrofluorimetric study, it was dem onstrated that the locust antidiuretic neurohormone, neuroparsin, enha nced cytosolic free Ca2+ concentrations, measured as percentages of th e ratio F405/F480 (R), in epithelial cells of the African locust rectu m. 5-hydroxytryptamine, whose antidiuretic effect was previously estab lished, enhanced R in longitudinal muscular cells, and was able to inc rease R slightly in epithelial cells. The possibility of reciprocal Ca 2+ movements between muscular and epithelial cells is discussed. Both of the neuronal molecules, which act via distinct transduction pathway s (phosphoinositide turnover for neuroparsin, and Ca2+-dependent adeny late cyclase for 5-hydroxytryptamine), stimulated an increase in R by causing Ca2+ entry through dihydropyridine-sensitive Ca2+ channels. Cy clic nucleotides (cAMP and cGMP) lowered R in epithelial cells, the cG MP effect being interpreted as a feedback control on phosphoinositide turnover and resulting in the ability to re-establish cAMP production to levels incompatible with high PLC activity. In longitudinal muscula r cells, the increase in R due to cAMP suggests the involvement of 5-h ydroxytryptamine in stimulation of adenylate cyclase activity. Further more, results enabled the localization in epithelial cells of the tran sduction pathways mediating the actions of another antidiuretic factor extracted from the glandular lobes of the locust corpora cardiaca.