title: Inhibition of carbonic anhydrase in the gills of two euryhaline crabs, Callinectes sapidus and Carcinus maenas, by heavy metals.
abstract: Two subcellular fractions of gill tissue, cytoplasm and basolateral membranes, from two species of euryhaline decapod crustaceans, Callinectes sapidus and Carcinus maenas, acclimated to low salinity, were isolated via differential centrifugation. Carbonic anhydrase activity from both fractions was titrated against a variety of heavy metals in vitro. The metals Ag(+), Cd(2+), Cu(2+) and Zn(+) showed inhibitory action against the enzyme. Ki values for these metals against cytoplasmic CA from C. sapidus were in the range of 0.05-0.5 microM (for Ag(+), Cd(2+) and Cu(2+)) and 2-6 microM for Zn(+), some of the highest sensitivities reported for CA from an aquatic organism. The Ki values for these same metals were approximately 2-3 orders of magnitude higher for cytoplasmic CA from C. maenas, indicating that there are significant differences in heavy metal sensitivity in branchial CA from the two species, and that C. maenas possesses a metal-resistant CA isoform. It required concentrations of metals in the millimolar range, however, to inhibit CA activity from the membrane fraction of the gill of both species. There were no effects on either mortality or on hemolymph osmotic and ionic concentrations in C. maenas that were exposed to 10 microM Cd or Zn(+) at 32 per thousand salinity and subsequently transferred to 10 per thousand. The presence of a metal-resistant CA isoform in the gills of C. maenas suggests that this species would not be restricted from its normal estuarine environment by heavy metal pollution.
authors.affiliation: Department of Biological Sciences, 131 Cary Hall, Auburn University, Auburn AL 36849, USA. henryp@auburn.edu
authors.forename: Hollie S
authors.initials: HS
authors.lastname: Skaggs
authors.forename: Raymond P
authors.initials: RP
authors.lastname: Henry
mesh_terms: D000818:Animals; D003386:Brachyura / Q000187:drug effects* / Q000201:enzymology; D002257:Carbonic Anhydrase Inhibitors / Q000494:pharmacology*; D002256:Carbonic Anhydrases / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D005880:Gills / Q000187:drug effects* / Q000201:enzymology; D008297:Male; D019216:Metals, Heavy / Q000494:pharmacology*
chemical_list: D002257:Carbonic Anhydrase Inhibitors; D019216:Metals, Heavy; D002256:Carbonic Anhydrases