Collapse of conductance is prevented by a glutamate residue conserved in voltage-dependent K(+) channels.
Voltage-dependent K(+) channel gating is influenced by the permeating ions. Extracellular K(+) determines the occupation of sites in the channels where the cation interferes with the motion of the gates. When external [K(+)] decreases, some K(+) channels open too briefly to allow the conduction of measurable current. Given that extracellular K(+) is normally low, we have studied if negatively charged amino acids in the extracellular loops of Shaker K(+) channels contribute to increase the local [K(+)]. Surprisingly, neutralization of the charge of most acidic residues has minor effects on gating. However, a glutamate residue (E418) located at the external end of the membrane spanning segment S5 is absolutely required for keeping channels active at the normal external [K(+)]. E418 is conserved in all families of voltage-dependent K(+) channels. Although the channel mutant E418Q has kinetic properties resembling those produced by removal of K(+) from the pore, it seems that E418 is not simply concentrating cations near the channel mouth, but has a direct and critical role in gating. Our data suggest that E418 contributes to stabilize the S4 voltage sensor in the depolarized position, thus permitting maintenance of the channel open conformation.
Departamento de Fisiología Médica y Biofísica, Facultad de Medicina y Hospital Universitario Virgen del Rocío, Universidad de Sevilla, Spain.
P
P
Ortega-Sáenz
R
R
Pardal
A
A
Castellano
J
J
López-Barneo
D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D004553:Electric Conductivity; D018698:Glutamic Acid / Q000737:chemistry; D015640:Ion Channel Gating / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed / Q000502:physiology; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000493:pharmacokinetics; D015221:Potassium Channels / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D051637:Shaker Superfamily of Potassium Channels
D015221:Potassium Channels; D051637:Shaker Superfamily of Potassium Channels; D018698:Glutamic Acid; D011188:Potassium