Carbonic anhydrase in branchial tissues of osmoregulating shore crabs, Carcinus maenas

Abstract

Activities of carbonic anhydrase (CA) were determined in various organs of shore crabs, Carcinus maenas, acclimated to salinities of 10, 20, 30, 40, and 50%0. In addition, some properties of the branchial enzyme (effects of detergents, storage conditions, and specific inhibitors) were tested. Subcellular distribution of gill CA was analyzed by means of centrifugation procedures. In hemolymph no CA activity could be detected. In all other organs except gills activities were low and insensitive to salinity change. High activities of CA were found in the gills. Activities in posterior gills were-in comparison with anterior gills-more than twofold increased. Acclimation of crabs to reduced ambient salinities resulted in significant increases in CA only in posterior gills. In the gill enzyme specific activities and stability during storage could be increased by means of the detergent Triton X-100 used a t 1% (viv) in the homogenizing medium. Sulfonamide inhibitors reduced CA activities effectively. Inhibition constants Ki of the gill enzyme were 7.0 x lo-' M for acetazolamide and 3.1 x lo-' M for methazolamide. Measurements of CA activities in supernatants and pellets obtained by differential centrifugation and in fractions obtained by centrifugation of 7,500g supernatants in a sucrose density gradient indicated that the major portion of CA activity in the gill (ca. 75%) was bound to celluIar particulates including plasma membranes and ca. 25% occurred in a soluble form in the cytoplasm. Both the bound and the soluble forms of CA were increased in crabs acclimated to low salinity, suggesting that CA in crab gills, besides its known role in C02 excretion and acid-base balance, functions in osmoregulatory processes.

The carbonic anhydrase of the Chinese crabEriocheir sinensis: Effects of adaption from tap to salt water

“…No activity could be detected in the hemolymph which is consistent with other investigations (Brinkman, 1933;Ferguson et al, 1937;Sobotka & Kann, 1941;Henry & Cameron, 1982;B6ttcher et al, 1990a). Only a little CA activity was measured in heart, hypodermis and antennal gland; values did not exceed 3 U/rag protein.…”

“…minerahzation of calcified structures, acid base balance and, last but not least, ion transport (Henry, 1988b). With regard to crabs, it has been reported that CA activity, which is mainly locahzed in the posterior gills, is induced during acclimation of the animals to diluted media (Henry & Cameron, 1982;B6ttcher et al, 1990a) suggesting its possible role in ion regulation. Recently, the results of electrophysiological studies of posterior gills of tap water-adapted Chinese crabs suggested a participation of branchial CA in ion transport.…”

Functional evidence for the presence of a carbonic anhydrase repressor in the eyestalk of the euryhaline green crabCarcinus maenas

“…This belief is based on evidence obtained primarily from two experimental model species, the blue crab Callinectes sapidus and the green crab Carcinus maenas. In both species, CA is found with high activities in the primary organ of ion transport, the gill (Henry and Cameron, 1982a;Bottcher et al, 1990;Henry et al, 2002). The current view of branchial CA function is that the enzyme catalyzes the hydration of respiratory CO 2 as it diffuses through the gills from the hemolymph to the surrounding water, resulting in the production of H + and HCO 3 -in the intracellular fluid.…”

Physiological role of branchial carbonic anhydrase in the shore crabCarcinus maenas

“…In light of extensive salinity-induced modification of CA activity in posterior gills of the hyper-regulating crab Callinectes sapidus, Henry and Cameron (1982 a) deduced that one of the potential roles of the enzyme is osmoregulation. In recent studies the CA of branchial tissues of crabs was shown to be localized in both the cytoplasm and the plasma membranes (Burnett and McMahon 1985, Henry 1987a, B6ttcher et al 1990a. In order to investigate the physiological roles of crab gill CA, techniques using intact individuals as well as isolated gill preparations were applied (Aldridge and Cameron 1979, Cameron 1979a, Burnett etal.…”