Physiological role of branchial carbonic anhydrase in the shore crabCarcinus maenas

Abstract

Abstract. Excretion of total CO2 and uptake of sodium and chloride ions across the branchial epithelium of the posterior gills of the shore crab Carcinus maenas, collected from Kiel Bay (Baltic Sea) in 1989, were measured using isolated perfused gill preparations. Total CO 2 effluxes depended on the HCO~-concentration of the internal perfusate in a saturable mode and were inhibited by internally and externally applied acetazolamide at 10-4 M. Potential differences between hemolymph space and medium did not change significantly during experimental treatments. Neither a bicarbonate gradient (6 mM) directed from the internal perfusate to external bath solution nor symmetrically applied 10-4 M acetazolamide significantly influenced the influxes of Na + and C1-. Results confirmed the role of carbonic anhydrase in CO 2 excretion but called into question the assumed functioning of the enzyme in branchial ion transport processes.

The impact of bleaching on the metabolic contribution of dinoflagellate symbionts to their giant clam host

“…As CO 2 diffuses across the membrane down a concentration gradient the CA maintains the bicarbonate/CO 2 equilibrium and therefore a continual supply of CO 2 for diffusion. In non‐symbiotic marine invertebrates CA is normally found on the cytosolic side of the gill epithelial plasma membrane (Böttcher et al . 1991) where it catalyses the conversion of bicarbonate to CO 2 , which then diffuses across the gill membrane and into the surrounding seawater.…”

“…As CO 2 diffuses across the membrane down a concentration gradient the CA maintains the bicarbonate/CO 2 equilibrium and therefore a continual supply of CO 2 for diffusion. In non-symbiotic marine invertebrates CA is normally found on the cytosolic side of the gill epithelial plasma membrane (Böttcher et al 1991) where it catalyses the conversion of bicarbonate to CO 2 , which then diffuses across the gill membrane and into the surrounding seawater. However, as the membrane CA (70 kDa isoform) is located on the extracellular side of the gills (Baillie & Yellowlees 1998; Leggat et al 2002) in giant clams there is little diffusion of C i from the haemolymph to the surrounding seawater.…”

The mechanism of sodium chloride uptake in hyperregulating aquatic animals

“…It was reported (Böttcher et al, 1991) that AZ had no effect on the (presumably transport-related) TEP in perfused gill of C. maenas, although it inhibited HCO3 -extrusion into the bathing medium. The apparent lack of effect on ion fluxes was confirmed, and a role for the enzyme in cell pH regulation was suggested (Siebers et al, 1994).…”

Multiple functions of the crustacean gill: osmotic/ionic regulation, acid-base balance, ammonia excretion, and bioaccumulation of toxic metals

“…While some transport proteins are species- and tissue-specific, the Na/K-ATPase and CA have a universal distribution among gills of crustaceans. However, both enzymes are present in the gills of euryhaline crustacean species in higher activity than in non-branchial tissue (e.g., Towle et al, 1976 ; Henry and Cameron, 1982a , b ; Siebers et al, 1982 ; D'Orazio and Holliday, 1985 ; Wheatly and Henry, 1987 ; Bottcher et al, 1991 ; Bouaricha et al, 1991 ; Henry, 1991 ; Lucu and Flik, 1999 ), and activities of both enzymes are higher in the gills of euryhaline species than in those of stenohaline, osmoconforming species (McDonough Spencer et al, 1979 ; Henry and Cameron, 1982a ; Henry, 1984 ; Harris and Bayliss, 1988 ). Furthermore, in euryhaline marine crustaceans, both enzymes have a heterogenous distribution among the gills.…”