Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology
On the mechanism of sodium-proton exchange in crayfish
Introduction
Due largely to the work of two laboratories, we have a compelling model for sodium uptake and proton extrusion in a pair of epithelial organs — the freshwater turtle urinary bladder and the frog skin. The model involves a diffusive sodium channel and an electrogenic proton pump in the apical membranes of specialized cells in the epithelia, as well as the Na+—K+ pump in the basal membrane. The ion flows across the apical membrane, both electrogenic, are coupled by the apical membrane potential producing an obligatory 1:1 exchange (Ehrenfeld et al., 1985, Steinmetz, 1986, Harvey, 1992).
Although the frog and the turtle are freshwater animals both are semi-terrestrial, a lifestyle that might have consequences for the operation of an apical ion exchange. Recently, attempts have been made to find evidence of this system in fully aquatic animals (fish), but the results have been ambiguous. A proton-ATPase was shown to be present in homogenates of rainbow trout gills (Lin and Randall, 1993). Antibody staining showed that the proton pump was located on the apical membrane (Lin et al., 1994). Probably the most convincing data have been obtained in very young fish. Bafilomycin, a specific inhibitor of the proton pump, inhibited sodium uptake in tilapia and carp (Fenwick et al., 1999) and also silver influx in trout (Bury and Wood, 1999). In the latter it was presumed that silver enters the cells through the sodium channel and that its entry is coupled to proton extrusion.
On the other hand, amiloride (0.1 mM), had little or no effect on proton efflux in rainbow trout (Lin and Randall, 1991); sodium uptake is completely abolished at this concentration. In addition, it has been shown that sodium–proton coupling was 1:1 in salt-depleted, intermolt crayfish and that amiloride abolished both fluxes as required by the current model (Kirschner et al., 1973, Ehrenfeld, 1974). However, such coupling could not be observed in tap water-adapted animals. There was net uptake of sodium but also net uptake of protons (or excretion of base), in untreated animals. Amiloride abolished the sodium flux, but it had a much smaller effect on proton movement (Ehrenfeld, 1974).
In this paper we pursue the question of transport mechanisms in crayfish. Much of the early work on Na+—H+ exchange in freshwater animals was done on salt-depleted animals. Since such animals must have an input of metabolic energy above that provided by the Na+—K+ pump on the basal membrane (discussed later), it is likely that they employ the system found in frog skin and turtle bladder. Ion fluxes in salt-depleted crayfish should, therefore, provide a useful basis for comparison with those in animals adapted to normal tap water.
Section snippets
Animals
Early experiments, including a few that employed dicycohexylcarbodiimide (DCCD) and N-ethylmaleimide (NEM), were carried out on intermolt Orconectes spp. obtained from a lake in Montana. All other work used intermolt Procambarus clarkii obtained from a commercial source (ATCHAFALAYA, Raceland, LA, USA). Control Na+ fluxes were larger in P. clarkii, but there were no differences between net Na+ and proton fluxes. O. spp. weighed between 20 and 30 g, P. clarkii between 30 and 50 g. The animals
Results
Net fluxes for Na+, TA, NH4+ and ΣH+ were measured in 58 TW-adapted crayfish; Jin(Na) in 55 of them. Net Cl− movement was measured in 28 of these animals. The data in Table 1 show that there was a significant Na+ influx. Net efflux of Na+ was significant (P<0.05), but very small, while Jnet (ΣH) was not significantly different from zero. The animals were obviously in, or very near, sodium and acid–base balance under these experimental conditions. However, there was a substantial Cl− efflux as
Discussion
Although it does not bear on the mechanism(s) of Na+ and proton movements, the imbalance among fluxes of Na+, H+ and Cl− in tap water-adapted animals requires explanation. The apparent inward movement of positive charge, shown in Table 1, is approximately equal to the efflux of Cl− and indicates that the latter was accompanied by the efflux of an unmeasured cation — a reasonable candidate is Ca2+. Two studies have shown that there is a net efflux of Ca2+ in TW-adapted crayfish amounting to as
References (29)
- et al.
H+/ATP Stoichiometry of proton pump of turtle urinary bladder
J. Biol. Chem.
(1980) Determination of ammonia and Kjeldahl nitrogen by indophenol method
Water Res.
(1976)- et al.
Kinetic analysis of electrogenic 2Na–1H antiport in crustacean hepatopancreas
Am. J. Physiol.
(1989) - et al.
Ion transport processes of crustacean epithelial cells
Physiol. Biochem. Zool.
(1999) - et al.
Electrogenic 2Na+/1H+ exchange in crustaceans
J. Memb. Biol.
(1990) - et al.
Cell and luminal activities of chloride, potassium, sodium and protons in the late distal tubule of necturus kidney
J. Physiol.
(1987) - et al.
Mechanism of branchial apical silver uptake by rainbow trout is via the proton-coupled Na+ channel
Am. J. Physiol.
(1999) - et al.
Inhibitory effect of modified bafilomycins and concanamycins on P- and V-type adenosinetriphosphatases
Biochemistry
(1993) Aspects of ionic transport mechanisms in crayfish Astacus leptodactylus
J. Exp. Biol.
(1974)- et al.
Electrogenic active proton pump in Rana esculenta skin and its role in sodium ion transport
J. Physiol.
(1985)
The key role of the H+ V-ATPase in acid–base balance and Na+ transport processes in frog skin
J. Exp. Biol.
In vivo bafilomycin-sensitive Na+ uptake in young freshwater fish
J. Exp. Biol.
Energization of sodium absorption by the H+-ATPase pump in mitochondria-rich cells of frog skin
J. Exp. Biol.
Intracellular ion activities in frog skin in relation to external sodium and effects of amiloride and/or ouabain
J. Physiol.
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