POWELL, MP*; WATTS, SA; HENRY, RP; Univ Alabama at Birmingham; Univ Alabama at Birmingham; Auburn Univ: Inhibition of branchial carbonic anhydrase induction in the euryhaline blue crab, Callinectes sapidus, by a repressor in the sinus gland
Blue crabs are euryhaline, being able to survive from 35 to 0 ppt salinity by regulating the osmotic concentration of the hemolymph above that of the ambient medium in waters below 27 ppt. Mechanisms of active ion transport are up-regulated in the posterior gills, which take up salts from dilute seawater. The enzyme carbonic anhydrase (CA) is a central molecular component of the ion uptake process. CA activity is induced 12 fold in posterior gills during transfer from 35 to 15 ppt in order to meet the demands of active ion transport. CA activity in anterior, respiratory gills, does not change. CA induction appears to be under hormonal regulation. Eyestalk ablation (ESA) resulted in CA induction in crabs acclimated to 35 ppt, and ESA potentiated normal low salinity-mediated CA induction. For intact crabs transferred from 35 to 15 ppt for 48 hr, injection of eyestalk extract resulted in a 40% reduction in normal CA induction. Furthermore, injection of extract from the major neurohemal organ of the eyestalk, the sinus gland, inhibited normal CA induction by 50%, whereas injection of extract from the remaining medullary tissue of the eyestalk had little effect. Pooled sinus glands, homogenized and extracted in acetonitrile, were separated by HPLC. The HPLC chromatogram was divided into four fractions (A-D). All fractions combined resulted in 40% inhibition of CA induction. Injection of fraction C, the fraction with the highest concentration of individual peaks, had the same inhibitory effect (40%) as did the pooled sinus glands; the remaining fractions had minimal effect. These results indicate CA induction is under inhibitory control by a CA repressor located in the sinus gland of the eystalk. Experiments are under way to isolate and identify this compound. Supported by NSF IBN 02-3005 to RPH.
