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

May 15, 2001The Journal of experimental zoology

Early increase of a salt-regulating enzyme in blue crab gills during low-salinity adjustment happens without changes in a related enzyme

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Abstract

CA induction in the gills of the blue crab, Callinectes sapidus, began within 24 hours of lowered salinity exposure.

Induction of carbonic anhydrase (CA) in the seventh gill pair increased with decreasing ambient salinity.
Activity in the third gill pair remained unchanged despite salinity changes.
The peak of CA induction occurred four days after exposure to low salinity.
Total ninhydrin-positive substances appeared in the hemolymph within 4 hours of low salinity transfer, indicating a cell volume regulatory response.
Ornithine decarboxylase (ODC) activity did not significantly change in gills of crabs acclimated to 35 ppt salinity.
A transient increase in ODC activity was observed in all tissues of crabs transferred from 28 ppt to 15 ppt, but this increase does not seem to influence CA induction.

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Carbonic anhydrase (CA) induction in the gills of the euryhaline blue crab, Callinectes sapidus, was measured in response to lowered environmental salinity. Simultaneous measurements of ornithine decarboxylase (ODC) activity were made in gills and nonbranchial tissues to determine whether ODC activity and the resultant synthesis of polyamines played a role in the initiation and regulation of CA induction. CA induction in the seventh gill pair (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 low salinity transfer, much earlier than previously reported, and peaked after 4 days. The magnitude of salinity change affected the magnitude of CA induction only, not the time course. A general cell volume regulatory response, as measured by the appearance of total ninhydrin-positive substances (TNPS) 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 initial signal in the pathway of CA induction. ODC activity in the gills of acclimated animals was not influenced by salinity. For crabs transferred from 35 to 25 ppt, ODC activity did not change significantly over the time course 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. Induction 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 regulation.

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

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