The enzyme carbonic anhydrase appears to be a central molecular component in the suite of physiological and biochemical adaptations to low salinity found in euryhaline crustaceans. It is present in high activities in the organs responsible for osmotic and ionic regulation, the gills, and more specifically, the individual gills that are specialized for active ion uptake from dilute sea water. Within those gills carbonic anhydrase is distributed among different subcellular pools, the cytoplasm, mitochondria and microsomes. The cytoplasmic pool represents the largest subcellular fraction of carbonic anhydrase activity, and it is this fraction that undergoes a tenfold induction during acclimation to low salinity. Carbonic anhydrase activity is present in excess of that needed to support the general ion-transport processes, and so it is doubtful that carbonic anhydrase activity itself is a point of short-term regulation in response to salinity changes. Rather, upregulation of carbonic anhydrase appears to be a result of selective gene expression, representing a permanent response to long-term adaptation to low salinity. The exact signal that initiates the induction of carbonic anhydrase, and the pathway through which that signal is transduced to the activation of the carbonic anhydrase gene, are unknown, but two promising avenues of research exist. First, induction of carbonic anhydrase is immediately preceded by hemodilution and subsequent cell swelling, a potential initiating event in the process. Second, recent work indicates that expression of carbonic anhydrase is under the control of a repressor substance, located in the eyestalk, whose effect is removed upon exposure to low salinity.

Bottcher
K.
,
Siebers
D.
,
Becker
W.
(
1990
).
Localization of carbonic anhydrase in the gills of Carcinus maenas.
Comp. Biochem. Physiol
96
,
243
–.
Bryan
G. W.
(
1960
).
Sodium regulation in the crayfish Astacus fluviatilis. I. The normal animal.
J. Exp. Biol
37
,
83
–.
Cioffi
M.
(
1984
).
Comparative ultrastructure of arthropod transporting epithelia.
Am. Zool
24
,
139
–.
Compere
P.
,
Wanson
S.
,
Pequeux
A.
,
Gilles
R.
,
Goffinet
G.
(
1989
).
Ultrastructural changes in the gill epithelium of the green crab Carcinus maenas in relation to the external salinity.
Tissue & Cell
21
,
299
–.
Copeland
D. E.
,
Fitzjarrell
A. T.
(
1968
).
The salt absorbing cells in the gills of the blue crab (Callinectes sapidus Rathbun) with notes on modified mitochondria.
Z. Zellforsch. Mikrosk. Anat
92
,
1
–.
Eckhardt
E.
,
Pierrot
C.
,
Thuet
P.
,
Van Herp
F.
,
Charmantier-Daures
M.
,
Trilles
J.-P.
,
Charmentier
G.
(
1995
).
Stimulation of osmoregulatingprocesses in the perfused gill of the crab Pachygrapsus marmoratus (Crustacea, Decapoda) by a sinus gland peptide.
Gen. Comp. Endocrinol
99
,
169
–.
Ehrenfeld
J.
(
1974
).
Aspects of ionic transport mechanisms in crayfish, Astacus leptodactylus.
J. Exp. Biol
61
,
57
–.
Evans
D. H.
,
Cameron
J. N.
(
1986
).
Gill ammonia transport.
J. Exp. Zool
239
,
17
–.
Finol
H. J.
,
Croghan
P. C.
(
1983
).
Ultrastructure of the branchial epithelium of an amphibious brackish-water crab.
Tissue & Cell
15
,
63
–.
Gehnrich
S.
,
Brooks
C.
,
Weihrauch
D.
,
Towle
D.
,
Henry
R.
(
2000
).
Alterations in carbonic anhydrase gene expression during low salinity adaptation in the shore crab, Carcinus maenas.
Bull. Mt Desert Island Biol. Lab
39
,
28
–.
Gehnrich
S.
,
Brooks
C.
,
Weirauch
D.
,
Towle
D.
,
Henry
R.
(
1999
).
Carbonic anhydrase gene expression in the gills of the shore crab during acclimation to low salinity.
Am. Zool
39
,
65
–.
Harris
R. R.
,
Andrews
M. B.
(
1985
).
Total NPS pool and ammonia net efflux rate changes in Carcinus maenas during acclimation to low salinity.
Comp. Biochem. Physiol
82
,
301
–.
Harris
R. R.
,
Micallef
H.
(
1971
).
Osmotic and ionic regulation in Potamon edulis, a fresh water crab from Malta
.
Comp. Biochem. Physiol
.
38A
,
769
776
.
Henry
R. P.
(
1984
).
The role of carbonic anhydrase in blood ion and acid—base regulation.
Am. Zool
24
,
241
–.
Henry
R. P.
(
1987
).
Membrane-associated carbonic anhydrase in the gills of the blue crab, Callinectes sapidus.
Am. J. Physiol
252
,
966
–.
Henry
R. P.
(
1988
).
Subcellular distribution of carbonic anhydrase activity in the gills of the blue crab, Callinectes sapidus.
J. Exp. Zool
245
,
1
–.
Henry
R. P.
(
1988
).
Multiple functions of gill carbonic anhydrase.
J. Exp. Zool
248
,
19
–.
Henry
R. P.
(
1996
).
Multiple roles of carbonic anhydrase in cellular transport and metabolism.
Annu. Rev. Physiol
58
,
523
–.
Henry
R. P.
,
Cameron
J. N.
(
1982
).
The distribution and partial characterization of carbonic anhydrase in selected aquatic and terrestrial decapod crustaceans.
J. Exp. Zool
221
,
309
–.
Henry
R. P.
,
Cameron
J. N.
(
1982
).
Acid—base balance in the euryhaline blue crab, Callinectes spidus, during acclimation from high to low salinity.
J. Exp. Biol
101
,
255
–.
Henry
R. P.
,
Cameron
J. N.
(
1983
).
The role of branchial carbonic anhydrase in respiration, ion regulation and acid—base balance in the aquatic crab, Callinectes sapidus and the terrestrial crab, Gecarcinus lateralis.
J. Exp. Biol
103
,
205
–.
Henry
R. P.
,
Campoverde
M. P.
,
Borst
D. W.
(
1999
).
Effects of eyestalk ablation on salinity-mediated carbonic anhydrase induction in three species of decapod crustaceans.
Am. Zool
39
,
65
–.
Henry
R. P.
,
Campoverde
M. P.
,
Borst
D. W.
(
2000
).
Effects of eyestalk ablation on carbonic anhydrase activity in the gills of Carcinus maenas and Cancer irroratus.
Bull. Mt Desert Island Biol. Lab
39
,
21
–.
Henry
R. P.
,
Garrelts
E. E.
,
McCarty
M. M.
,
Towle
D. W.
(
1999
).
Salinity adaptations in the euryhaline green crab, Carcinus maenas.
Bull. Mt Desert Island Biol. Lab
38
,
55
–.
Henry
R. P.
,
Mangum
C. P.
(
1980
).
Salt and water balance in the oligohaline clam, Rangia cuneata. I. Anisosomotic extracellular regulation.
J. Exp. Zool
211
,
1
–.
Henry
R. P.
,
Smatresk
N. J.
,
Cameron
J. N.
(
1988
).
The distribution of branchial carbonic anhydrase and the effects of gill and erythrocyte carbonic anhydrase inhibition in the channel catfish Ictalurus punctatus.
J. Exp. Biol
134
,
201
–.
Lin
H.
,
Randall
D. J.
(
1991
).
Evidence for the presence of an electrogenic proton pump on the trout gill epithelium.
J. Exp. Biol
161
,
119
–.
Lucu
C.
,
Flik
G.
(
1999
).
Na+/K+-ATPase and Na+/Ca2+exchange activities in gills of hyperregulating Carcinus maenas.
Am. J. Physiol
276
,
490
–.
Maren
T. H.
(
1967
).
Carbonic anhydrase: chemistry, physiology and inhibition.
Physiol. Rev
47
,
595
–.
Neufeld
G. J.
,
Holliday
C. W.
,
Pritchard
J. B.
(
1980
).
Salinity adaptation of gill Na/K in the blue crab, Callinectes sapidus.
J. Exp. Zool
211
,
215
–.
Pierce
S. K.
,
Amende
L. M.
(
1981
).
Control mechanisms of amino acid-mediated cell volume regulation in salinity-stressed molluscs.
J. Exp. Zool
215
,
247
–.
Piller
S. C.
,
Henry
R. P.
,
Doeller
J. E.
,
Kraus
D. W.
(
1995
).
A comparison of the gill physiology of two euryhaline crab species, Callinectes sapidus and Callinectes similis: energyproduction, transport-related enzymes and osmo-regulation as a function of acclimation salinity.
J. Exp. Biol
198
,
349
–.
Riestenpatt
S.
,
Onken
H.
,
Siebers
D.
(
1996
).
Active absorption of Na+and Clacross the gill epithelium of the shore crab Carcinus maenas: voltage-clamp and ion-flux studies.
J. Exp. Biol
199
,
1545
–.
Savage
J. P.
,
Robinson
G. D.
(
1983
).
Inducement of increased gill Na+-K+ATPase activity by a hemolymph factor in1002hyperosmoregulating Callinectes sapidus.
Comp. Biochem. Physiol
75
,
65
–.
Sommer
M. J.
,
Mantel
L. H.
(
1988
).
Effect of dopamine, cyclic AMP and pericardial organs on sodium uptake and Na/K-ATPase activity in gills of the green crab Carcinus maenas (L.).
J. Exp. Zool
248
,
272
–.
Spannings-Pierrot
C.
,
Soyez
D.
,
Van Harp
F.
,
Charmantier
G.
(
1999
).
Involvement of CHH in the control of osmoregulation in a grapsid crab.
Am. Zool
39
,
68
–.
Towle
D. W.
(
1984
).
Membrane-bound ATPases in arthropod ion-transporting tissues.
Am. Zool
24
,
177
–.
Towle
D. W.
(
1997
).
Molecular approaches to understanding salinity adaptation of estuarine animals.
Am. Zool
37
,
575
–.
Towle
D. W.
,
Palmer
G.
,
Harris
J.
(
1976
).
Role of gill Na++K+-dependent ATPase in acclimation of blue crabs (Callinectes sapidus) to low salinity.
J. Exp. Zool
196
,
315
–.
Towle
D. W.
,
Rushton
M. E.
,
Heidysch
D.
,
Magnani
J. J.
,
Rose
M. J.
,
Amstutz
A.
,
Jordan
M. K.
,
Shearer
D. W.
,
Wu
W.-S.
(
1997
).
Sodium/proton antiporter in the euryhaline crab Carcinus maenas: molecular cloning, expression and tissue distribution.
J. Exp. Biol
200
,
1003
–.
Wheatly
M. G.
,
Henry
R. P.
(
1987
).
Branchial and antennal gland Na+/K+-dependent ATPase and carbonic anhydrase activity during salinity acclimation of the euryhaline crayfish Pacifastacus leniusculus.
J. Exp. Biol
133
,
73
–.
Zanders
I. P.
(
1980
).
Regulation of blood ions in Carcinus maenas (L.).
Comp. Biochem. Physiol
65
,
97
–.
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