AJP - Regulatory, Integrative and Comparative Physiology, Vol 242, Issue 5 505-R513, Copyright © 1982 by American Physiological Society
Neuroendocrine control of Na+ balance in the fiddler crab Uca pugilator
C. W. Davis and I. R. Hagadorn
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.
