Meeting Abstract

P1.82  Jan. 4  Down-regulation of carbonic anhydrase activity and expression in the gills of Carcinus maenas in response to high salinity JILLETTE, N*; CAMMACK, L; HENRY, RP; Mt Desert Island Biol. Lab; Auburn Univ; Auburn Univ henryrp@auburn.edu

Branchial carbonic anhydrase (CA) is up-regulated in the ion-transporting gills of the green crab in response to low salinity exposure when the animal makes its annual migration into estuarine waters. There have been no studies, however, on whether CA is then down-regulated when the green crab returns to high salinity. Green crabs, acclimated to 32 ppt, were transferred to 15 ppt for 1 wk. Hemolymph osmolality, and branchial CA activity and CA mRNA expression were then measured in a sub-set of crabs. The remaining crabs were transferred back to 32 ppt and sampled weekly as above for a period of 5 wks. For crabs transferred from 15 to 32 ppt, hemolymph osmolality rose quickly and stabilized by 24 hr after transfer at values close to those for ambient seawater. CA mRNA expression was induced by about 6 fold after 1 wk in 15 ppt, but these values returned to low, baseline values found in 32 ppt acclimated crabs within 1 wk of being transferred back to 32 ppt, and they remained low for the 5 wk duration of the experiment. CA activity was induced 5 fold at 15 ppt, but high levels of activity persisted for 4 wks after transfer back to 32 ppt. CA activity did not return to baseline, high salinity acclimated levels until 5 wks at 32 ppt. So while changes CA mRNA expression are rapid in response to both low and high salinity exposure, changes in CA activity occur more slowly. In particular, once synthesized, the CA protein appears to have a long biological life span in the gill, presumably because the new protein represents a large and expensive metabolic commitment. Supported by NSF 02-30005 to RPH and by an INBRE award to MDIBL.