BURGENTS, J.E.; LOVETT, D.L.*: Is the increase in Na⁺,K⁺-ATPase activity observed during hyperosmoregulation in the blue crab Callinectes sapidus due to stimulation of translation?

Estuarine crabs such as the blue crab Callinectes sapidus hyperosmoregulate in dilute seawater through transport of ions across the gill epithelium by the enzyme Na⁺,K⁺-ATPase (ATPase). It has been well documented that the relative activity of ATPase in gills is higher in crabs acclimated to low salinity than in crabs acclimated to high salinity. In previous studies, we have shown that ATPase activity in gill homogenates increases significantly by 4 days after transfer to dilute sea water and reaches a maximum between 6 and 8 days. By the time the crab has acclimated to low salinity (approximately 18 days after transfer) the activity has decreased slightly from this maximum. This increase in activity during acclimation to low salinity may be due to synthesis of new enzyme or activation or deinhibition of existing enzyme. Using immunological techniques to quantify the amount of α5-subunit of ATPase present, we determined that the amount of ATPase in gill tissue changes in a pattern that is reflective of the pattern observed for change in ATPase activity. This trend was observed using both the total amount of protein in the homogenate and the amount of actin in the homogenate to control for variations in homogenation or dilution of samples. Thus, the amount of ATPase protein present does appear to change during acclimation. We currently are attempting to measure the relative amount of mRNA coding for the α-subunit of ATPase to determine whether significant change in mRNA expression occurs during acclimation to dilute sea water.