Serotonin regulation of gill cAMP production, Na, and water uptake in freshwater mussels

Abstract

Abstract Active Na transport in freshwater mussels was stimulated by addition of 10 −4 M serotonin (5‐HT) in the bath. Carrier kinetics apply to serotonin‐stimulated Na uptake with no effect on the affinity (K m 10 −4 M). The J max i was increased 350% over controls to 5.83 μeq (g dry tissue · h) −1 . Amiloride reversibly inhibited the 5‐HT‐stimulated Na influx. Serotonin also caused a net water uptake of 0.36 ml H 2 O (g dry tissue · h) −1 , due, in part, to a reduction in renal filtration. When mussel gill tissue was incubated in pondwater containing 10 −4 M 5‐HT, cAMP content increased 2.5 times control levels within the first minute and then declined toward control values by 20 minutes. Theophylline (10 −3 M) in the incubation medium prevented this decline. Dopamine, epinephrine, or norepinephrine (10 −4 M in pondwater) increased gill cAMP concentrations; L‐dopa did not. Both 5‐HT and dopamine significantly increased gill cAMP concentration at 10 −5 M.