Sodium uptake and transport (Na + + K +)ATPase changes following Na + depletion and low salinity acclimation in the mangrove crab Ucides cordatus (L.)

Abstract

1. 1. Ucides cordatus in a medium isoionic for Na + and isosmotic with the haemolymph (26% o salinity) has a relatively small active uptake component of Na + influx (7% of J in). 2. 2. In 9% o medium (hypo-osmotic to the haemolymph) Na + is maintained by increased active uptake of Na + (to 75% of J in). 3. 3. Short-term Na + depletion of animals acclimated to either medium stimulated active sodium uptake, increasing this component 4–5-fold. 4. 4. The net increase in active uptake was similar in both 26 and 9% o acclimated animals (~6μM g/hr), although the maximum rate was higher in the latter. 5. 5. After acclimation to 9% o (120hr), increases in gill and antennal gland (Na + + K +)-ATPases were observed, notably in the posterior gill pairs. 6. 6. Mechanisms for the rapid Na + depletion response and that of longer-term acclimation to low salinities in this euryhaline mangrove crab are discussed.