Neuroendocrine control of Na+ balance in the fiddler crab Uca pugilator.
The hemolymph ionic composition and unidirectional Na+ fluxes were analyzed in fiddler crabs (Uca) acclimated to 500 mosmol seawater. Eyestalkless crabs had lower hemolymph osmotic, Na+, and Cl- concentrations. The Na+ efflux was increased from 13.6  +/- 0.6 in control crabs to 19.6 +/- 1.3 mueq.g-1.h-1 in eyestalkless crabs; this increase was shown to be due to a higher Na+ permeability in eyestalkless crabs. Hemolymph Na+ in eyestalkless crabs was increased by an injection of eyestalk extract. The Na+ influx was increased from 11.1 in intact to 15.8 mueq.g-1.h-1 in eyestalkless animals. A kinetic study showed that 1) the influx was higher at all external Na+ concentrations in eyestalkless and intact-Na+-depleted crabs than in intact controls, and 2) the influx mechanism exhibited allosterism. The elevated Na+ influx in eyestalkless crabs was decreased by an injected eyestalk extract. An injected brain extract caused in increase in the Na+ influx in intact animals. It is concluded that the Na+ uptake mechanism is activated by decreasing the hemolymph Na+ concentration and that a brain hormone mediates the effect.
D000818:Animals; D003386:Brachyura / Q000502:physiology*; D002490:Central Nervous System / Q000502:physiology*; D002712:Chlorides / Q000032:analysis; D004702:Endocrine Glands / Q000502:physiology*; D006458:Hemolymph / Q000032:analysis; D007700:Kinetics; D012964:Sodium / Q000032:analysis / Q000378:metabolism*; D014020:Tissue Extracts / Q000494:pharmacology
D002712:Chlorides; D014020:Tissue Extracts; D012964:Sodium