Na+ promotes the dissociation between Galpha GDP and Gbeta gamma, activating G protein-gated K+ channels.
J Biol Chem
; 278(6): 3840-5, 2003 Feb 07.
Article
en En
| MEDLINE
| ID: mdl-12488455
G protein-gated K(+) channels (GIRK, or Kir3) are activated by the direct binding of Gbetagamma or of cytosolic Na(+). Na(+) activation is fast, Gbetagamma-independent, and probably via a direct, low affinity (EC(50), 30-40 mm) binding of Na(+) to the channel. Here we demonstrate that an increase in intracellular Na(+) concentration, [Na(+)](in), within the physiological range (5-20 mm), activates GIRK within minutes via an additional, slow mechanism. The slow activation is observed in GIRK mutants lacking the direct Na(+) effect. It is inhibited by a Gbetagamma scavenger, hence it is Gbetagamma-dependent; but it does not require GTP. We hypothesized that Na(+) elevates the cellular concentration of free Gbetagamma by promoting the dissociation of the Galphabetagamma heterotrimer into free Galpha(GDP) and Gbetagamma. Direct biochemical measurements showed that Na(+) causes a moderate decrease (approximately 2-fold) in the affinity of interaction between Galpha(GDP) and Gbetagamma. Furthermore, in accord with the predictions of our model, slow Na(+) activation was enhanced by mild coexpression of Galpha(i3). Our findings reveal a previously unknown mechanism of regulation of G proteins and demonstrate a novel Gbetagamma-dependent regulation of GIRK by Na(+). We propose that Na(+) may act as a regulatory factor, or even a second messenger, that regulates effectors via Gbetagamma.
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Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
Sodio
/
Canales de Potasio
/
Activación del Canal Iónico
/
Proteínas de Unión al GTP
Tipo de estudio:
Prognostic_studies
Límite:
Animals
Idioma:
En
Revista:
J Biol Chem
Año:
2003
Tipo del documento:
Article
País de afiliación:
Israel
Pais de publicación:
Estados Unidos