Early carbonic anhydrase induction in the gills of the blue crab, Callinectes sapidus, during low salinity acclimation is independent of ornithine decarboxylase activity

Carbonic anhydrase (CA) induction in the gills of the euryhaline blue crab, Callinectes sapidus, was measured in response to lowered environmental sal inity. Simultaneous measurements of ornithine decarboxylase (ODC) activity were made in gills and nonbranchial tissues to determine whether ODC activi ty and the resultant synthesis of polyamines played a role in the initiatio n and regulation of CA induction. CA induction in the seventh gill pail (G7 ) was proportional to the decrease in ambient salinity, but activity in the third gill pair (G3) remained unchanged. Induction began by 24 hr after lo w salinity transfer, much earlier than previously reported, and peaked afte r 4 days. The magnitude of salinity change affected the magnitude of CA ind uction only, not the time course. A general cell volume regulatory response , as measured by the appearance of total ninhydrin-positive substances (TNP S) in the hemolymph, was initiated within 4 hr of low salinity transfer and was complete by 24 hr post-transfer. General cell swelling may be the init ial signal in the pathway of CA induction. ODC activity in the gills of acc limated animals was not influenced by salinity. For crabs transferred from 35 to 25 ppt, ODC activity did not change significantly over the time cours e of acclimation. There was an early but transient increase in ODC activity in all tissues for crabs acclimated to 28 ppt and transferred to 15 ppt. I nduction of ODC activity does not appear to be a precursor for CA induction ; therefore, it does not appear that polyamines are substantially involved in the up-regulation of transport enzyme activity in low salinity. ODC, and resultant polyamine synthesis, may, however, have a role in cell volume re gulation. J. Exp. Zool. 289:350-358, 2001. (C) 2001 Wiley-Liss, Inc.