Inhibition of Na super(+)/K super(+)-ATPase and of active ion-transport functions in the gills of the shore crab Carcinus maenas induced by cadmium

• Published in: Marine biology 1998-02, Vol.130 (3), p.407-416
• Main Authors: Postel, U, Petrausch, G, Riestenpatt, S, Weihrauch, D, Malykh, J, Becker, W, Siebers, D
• Format: Article
• Language: English
• Subjects: Carcinus maenas; Marine
• ISSN: 0025-3162
• DOI: 10.1007/s002270050261

Inhibition of Na super(+)/K super(+)-ATPase from gill plasma membranes of the shore crab Carcinus maenas by cadmium was investigated and compared with inhibitory effects by known antagonists (ouabain and Ca super(2+)). For comparative considerations the Cd super(2+)-inhibition of the enzyme from dog kidney was also tested. Na super(+)/K super(+)-ATPase from dog kidney and from crab gill differed greatly in sensitivity against ouabain. The inhibition constant K sub(i) of the dog enzyme amounted to 9.1 x 10 super(-7) mol l super(-1), i.e. more than 300-fold smaller than the K sub(i) of 2.9 x 10 super(-4) mol l super(-1) determined for the crab enzyme. Ca super(2+) inhibited the activity of Na super(+)/K super(+)-ATPase from crab gill plasma membranes with a K sub(i) of 4.3 x 10 super(-4) mol l super(-1). The Na super(+)/K super(+)-ATPase from crab gill was inhibited by Cd super(2+) with a K sub(i) of 9.1 x 10 super(-5) mol l super(-1). Cd super(2+) inhibited the Na super(1)/K super(1)-ATPase from dog kidney with a K sub(i) (6.4 x 10 super(-5) mol l super(-1)) comparable to that observed in the crab gill enzyme. Under experimental conditions Cd super(2+)-inhibition of Na super(+)/K super(+)-ATPase was irreversible. Repeated washing, centrifugation and homogenization of the plasma membranes (four times) with Cd super(2+)-free buffer did not restore any activity lost in the presence of 1 x 10 super(-3) mol l super(-1) Cd super(2+). Since ouabain-insensitive (nonspecific) ATPases in the plasma membrane fraction of crab gills were inhibited by Cd super(2+) in the same way as Na super(+)/K super(+)-ATPase, the heavy metal is considered as an unspecific ATPase inhibitor. Comparing these results with literature data on Cd super(2+)-binding to electrophoretically separated proteins suggests that Na super(+)/K super(+)-ATPase is a Cd super(2+)-binding enzyme. The results obtained on Na super(+)/K super(+)-ATPase were reflected by Cd super(2+)-inhibition of the branchial ion-transport functions depending on this enzyme. The transpithelial short-circuit current of isolated gill half lamellae, a direct measure of area-specific active ion uptake, and the transepithelial potential difference of isolated, perfused whole gills, also indicative of active ion uptake, were inhibited by the heavy metal in a time- and dose-dependent mode. Remarkably these inhibitions were also irreversible. These findings are ecologically and biomedically significant: even when the actual environ