Cyclic AMP as a modulator of NaCl transport in gills of the euryhaline Chinese crabEriocheir sinensis

Experiments on the effect of cyclic AMP on Na+ and Cl− transport pathways were performed on isolated, perfused preparations of the posterior, osmoregulating gills of the euryhaline Chinese crabEriocheir sinensis. The crabs were caught during the autumn of 1987 in freshwater lakes near Emden (Federal Republic of Germany). N6-2′-O-dibutyryl adenosine 3′:5′-cyclic monophosphate (db-cAMP), 3-isobutyl-1-methylxanthine (IBMX), and 7β-acetoxy-8,13-epoxy-1α, 6β, 9α-trihydroxy-labd-14-ene-11-one (forskolin) induce an increase in the influx of both Na+ and Cl− in the gills. They also induce significant hyperpolarization. This last result indicates that the increase in NaCl uptake is related to an activation of both the Na+/K+ pump and the Cl−channels located at the serosal side of the gill epithelium. The possibility that cAMP acts as a second messenger, mediating the effects of different neuroendocrine factors involved in ionic and osmotic regulation in crustaceans is discussed.