Separable gating mechanisms in a Mammalian pacemaker channel.
J Biol Chem
; 277(39): 35939-46, 2002 Sep 27.
Article
em En
| MEDLINE
| ID: mdl-12121985
ABSTRACT
Despite permeability to both K(+) and Na(+), hyperpolarization-activated cyclic nucleotide-gated (HCN) pacemaker channels contain the K(+) channel signature sequence, GYG, within the selectivity filter of the pore. Here, we show that this region is involved in regulating gating in a mouse isoform of the pacemaker channel (mHCN2). A mutation in the GYG sequence of the selectivity filter (G404S) had different effects on the two components of the wild-type current; it eliminated the slowly activating current (I(f)) but, surprisingly, did not affect the instantaneous current (I(inst)). Confocal imaging and immunocytochemistry showed G404S protein on the periphery of the cells, consistent with the presence of channels on the plasma membrane. Experiments with the wild-type channel showed that the rate of I(f) deactivation and I(f) amplitude had a parallel dependence on the ratio of K(+)/Na(+) driving forces. In addition, the amplitude of fully activated I(f), unlike I(inst), was not well predicted by equal and independent flow of K(+) and Na(+). The data are consistent with two separable gating mechanisms associated with pacemaker channels one (I(f)) that is sensitive to voltage, to a mutation in the selectivity filter, and to driving forces for permeating cations and another (I(inst)) that is insensitive to these influences.
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Base de dados:
MEDLINE
Assunto principal:
Canais Iônicos
/
Proteínas Musculares
Idioma:
En
Ano de publicação:
2002
Tipo de documento:
Article