100% SW-acclimated crabs were abruptly
transferred to 50% SW and Na, K-ATPase ESA of the
sixth gill and hemolymph osmotic pressures were measured
for 14 d (Fig. 5). Although hemolymph osmotic pressure
decreased rapidly and was significantly lower than control
values after only 12 h, branchial Na, K-ATPase ESA did
not increase significantly from control values until 3 d after
transfer. This time course is consistent with both rapid
modulation of existing Na, K-ATPase activity in branchial
ion transport cells in the short term and a longer-term
increase in the amount of enzyme present in the cells.