Kinetic mechanism of inhibition of the Na+-pump and some of its partial reactions by external Na+ (Na+o).
J Theor Biol
; 134(2): 165-82, 1988 Sep 17.
Article
en En
| MEDLINE
| ID: mdl-2854181
ABSTRACT
The effects of external Na+ on the activity of the Na+-pump are complex. The first-order rate constant for Na+-efflux is reduced in the presence of very low external Na+ concentrations, and this inhibition is reversed when the Na+ level is raised. The same pattern has been observed for Na+-ATPase activity; however, it is not apparent from the current reaction mechanisms at which site (or sites) external Na+ binds to cause inhibition. In this paper, the effect of external Na+ on Na+-pump activity was studied by simulation, using a model similar to the Post-Albers scheme. Curves similar to those experimentally observed were obtained assuming that (i) after phosphorylation, three Na+ ions are translocated and consecutively released to the external medium with decreasing dissociation constants; (ii) external Na+, with low affinity, binds to the K+o (external) sites stimulating dephosphorylation. These assumptions also permit one to explain the experimental observation that external Na+ (with both high and low affinities) competes with K+, inhibiting the K+ influx due to the Na+-pump, and the kinetically similar behavior of Na+-ATPase and ATP/ADP exchange reactions at low variable Na+ concentrations. The experimental evidence available that supports the present hypothesis is discussed.
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Colección:
01-internacional
Banco de datos:
MEDLINE
Asunto principal:
Sodio
/
Canales de Sodio
Tipo de estudio:
Prognostic_studies
Límite:
Animals
/
Humans
Idioma:
En
Revista:
J Theor Biol
Año:
1988
Tipo del documento:
Article