US EPA

4970678 

Journal Article 

Mercury Inhibits Na-K-ATPase Primarily at the Cytoplasmic Side 

Anner, BM; Moosmayer, M 

1992 

Yes 

American Journal of Physiology
ISSN: 0002-9513
EISSN: 2163-5773 

262 

5 

The site of action of the inhibition of sodium/potassium dependent adenosine-triphosphatase (NaKATPase) activity by mercury (7439976) was investigated. A two sided test system consisting of artificially formed phospholipid vesicles (liposomes) containing purified NaKATPase molecules prepared from rabbit kidneys in right side out (RSO) or inside out (ISO) orientations was used. The system was incubated with 0 to 100 micromolar (microM) mercuric-chloride (7487947) or 0 to 1000microM convallatoxin (508758) in the presence or absence of 10 millimolar (mM) adenosine-triphosphate (ATP). In some experiments, the liposomes had been preloaded with rubidium-86 (Rb-86). The effects on active sodium-ion and potassium-ion transport were assessed by measuring uptake or efflux of Rb-86 from the prelabeled system. In control liposomes prelabeled with Rb-86 through the RSO pumps, ATP caused the radioactivity to leak out through the ISO pumps. Convallatoxin at 1microM completely inhibited Rb-86 uptake through the RSO pumps. At 100microM it completely inhibited Rb-86 efflux through the ISO pumps. No Rb-86 efflux was observed after treatment with 1000microM convallatoxin. At 1microM, mercuric-chloride had no effect on Rb-86 transport, but at 10microM it inhibited 90% of the Rb-86 transport through the ISO pumps. Partial inhibition of the RSO pumps was induced by 25microM mercuric-chloride and inhibition was seen for both pumps with a dose of 50microM mercuric-chloride. Treatment with 100microM mercuric-chloride caused more than 50% of the Rb-86 to leak out. This was taken as evidence that the structure of the NaKATPase molecule had been disrupted by mercury. Calibration experiments performed with the liposome system were described. The authors conclude that the metal binding interface of the NaKATPase molecule is involved in active ion transport and that the cytoplasm of the NaKATPase molecule is the primary target for mercury. The cellular transport mechanism for mercuric-chloride is different from that of convallatoxin and other cardioactive steroids.