HENRY, R.P.*; SMITH, C.; Auburn Univ.; Unov. of New Hampshire: Functional characteristics of a carbonic anhydrase repressor in the eyestalk of the euryhaline green crab, Carcinus maenas.

The enzyme carbonic anhydrase (CA) is induced 8-12 fold in the posterior, ion transporting gills of euryhaline crustaceans during low salinity acclimation. In the green crab, there is an initial doubling of CA activity at 96 hr after transfer from 32 to 10 ppt salinity, with new acclimated levels being reached by 7 days post-transfer. Eyestalk ablation (ESA) results in a 50% increase in CA activity in posterior gills of crabs acclimated to 32 ppt; and this effect is eliminated when crabs treated with ESA are given daily injections of eyestalk homogenates. ESA prior to low salinity transfer potentiates the normal CA induction by about 30%. These results suggest the presence of a CA repressor, present in the eyestalks at high salinity, which keeps CA expression at minimal levels, and whose effects are removed during low salinity acclimation, allowing CA induction to occur. Further experiments have supported this idea. Injections of eyestalk homogenates from crabs acclimated to 32 ppt into crabs transferred to 10 ppt inhibit normal CA induction by 50-70%. Similar experiments, but using eyestalks from 10 ppt acclimated crabs, resulted in only a 20% inhibition of CA induction, suggesting that the putative CA repressor is down-regulated in low salinity. This is supported by the fact that ESA in 10 ppt acclimated crabs has little effect on CA activity. The CA repressor also appears to be present only in euryhaline species, as injections of eyestalk homogenates from a stenohaline species, Cancer irroratus, has no inhibitory effect on CA induction in C. maenas. Supported by NSF IBN 02-30005.