Modulation of pump function by mutations in the first transmembrane region of Na(+)-K(+)-ATPase alpha 1-subunit.
The Cys in the first transmembrane region of the Na(+)-K(+)-adenosinetriphosphatase (ATPase) alpha 1-subunit has been shown to be a critical determinant of cardiac glycoside binding. To study the role of this Cys on ion transport activity, we measured pump currents in HeLa cells expressing wild-type or mutant alpha 1-subunit cDNAs. The endogenous ouabainsensitive Na(+)-K(+)-ATPase was selectively inhibited by growing the cells in 0.1 microM ouabain. A Cys-to-Tyr substituted mutant exhibited decreased sensitivity to digitoxin but not digoxin compared with wild type. The decreased affinity for digitoxin was due to a faster dissociation rate. In contrast, the Cys-to-Ala substitution did not significantly alter the sensitivity to digitoxin or digoxin. Both wild-type and mutant cells displayed marked external K(+)-dependent pump currents; however, the affinity for K+ was reduced by the mutations. The decrease in K+ affinity was due to a slower association rate. The results show that the Cys that interacts with cardiac glycosides also participates in the sensitivity of the pump to external K+.
Yamamoto
S
S
Department of Pharmacology and Cell Biophysics, University of Cincinnati College of Medicine, Ohio 45267, USA.
Askew
G R
GR
Heiny
J
J
Masaki
H
H
Yatani
A
A
D000595:Amino Acid Sequence; D002301:Cardiac Glycosides / Q000494:pharmacology; D004553:Electric Conductivity; D006367:HeLa Cells / Q000187:drug effects / Q000201:enzymology; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics* / Q000502:physiology*
D002301:Cardiac Glycosides; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium