HENRY, R.P.: Suppression of salinity-sensitive branchial carbonic anhydrase induction by a compound in the eyestalk of the euryhaline green crab, Carcinus maenas.
Carbonic anhydrase activity in the posterior gills of the euryhaline green crab, Carcinus maenas, undergoes an 8 fold induction upon transfer from 32 to 12 ppt salinity. Eyestalk ablation (ESA) results in a 50% increase in CA activity even in the absence of a salinity change, and a 20% increase in activity after salinity transfer. Crabs were treated with ESA and subsequently injected daily for 7 days with supernatant of crude eyestalk homogenate, the equivalent of two eyestalks per day. Crabs acclimated to 32 ppt, treated with ESA and injections, had no increase in CA activity; values were similar to control animals injected with sea water. Injection of eyestalk extract also suppressed CA induction in crabs treated with ESA and low salinity exposure. CA activity in the posterior gills was significantly lower than in uninjected animals. Furthermore, injection of eyestalk extract suppressed CA induction by 50% in intact crabs (no ESA treatment) exposed to low salinity. These results point to the presence of a substance in the eyestalk that functions to suppress CA expression at high salinity. Suppression is removed upon exposure to low salinity, and treatment with ESA enhances that effect. Adding back the substance through injection of eyestalk extract not only reverses the effects of ESA, but it also prevents the normal low salinity-mediated induction of CA in intact crabs. Supported by NSF IBN 97-27835.