Voltage-dependent opening of HCN channels: Facilitation or inhibition by the phytoestrogen, genistein, is determined by the activation status of the cyclic nucleotide gating ring.
Biochim Biophys Acta
; 1788(9): 1939-49, 2009 Sep.
Article
em En
| MEDLINE
| ID: mdl-19524546
ABSTRACT
Investigation of the mechanistic bases and physiological importance of cAMP regulation of HCN channels has exploited an arginine to glutamate mutation in the nucleotide-binding fold, an approach critically dependent on the mutation selectively lowering the channel's nucleotide affinity. In apparent conflict with this, in intact Xenopus oocytes, HCN and HCN-RE channels exhibit qualitatively and quantitatively distinct responses to the tyrosine kinase inhibitor, genistein -- the estrogenic isoflavonoid strongly depolarizes the activation mid-point of HCN1-R538E, but not HCN1 channels (+9.8 mV + or - 0.9 versus +2.2 mV + or - 0.6) and hyperpolarizes gating of HCN2 (-4.8 mV + or - 1.0) but depolarizes gating of HCN2-R591E (+13.2 mV + or - 2.1). However, excised patch recording, X-ray crystallography and modeling reveal that this is not due to either a fundamental effect of the mutation on channel gating per se or of genistein acting as a mutation-sensitive partial agonist at the cAMP site. Rather, we find that genistein equivalently moves both HCN and HCN-RE channels closer to the open state (rendering the channels inherently easier to open but at a cost of decreasing the coupling energy of cAMP) and that the anomaly reflects a balance of these energetic effects with the isoform-specific inhibition of activation by the nucleotide gating ring and relief of this by endogenous cAMP. These findings have specific implications with regard to findings based on HCN-RE channels and kinase antagonists and general implications with respect to interpretation of drug effects in mutant channel backgrounds.
Texto completo:
1
Base de dados:
MEDLINE
Assunto principal:
Canais de Potássio
/
Ativação do Canal Iônico
/
AMP Cíclico
/
Genisteína
/
Canais de Cátion Regulados por Nucleotídeos Cíclicos
Tipo de estudo:
Prognostic_studies
Limite:
Animals
Idioma:
En
Ano de publicação:
2009
Tipo de documento:
Article