Inactivation determined by a single site in K+ pores.
An N-terminus peptide or a C-terminus mechanism involving a single residue in transmembrane segment 6 produces inactivation in voltage-dependent K+ channels. Here we show that a single position in the pore of K+ channels can produce inactivation having characteristics distinct from either N- or C-type inactivation. In a chimeric K+ channel (CHM), the point reversion CHM V369K produced fast inactivation and CHM V369S had the additional effect of halving K+ conductance consistent with a position in the pore. The result was not restricted to CHM; mutating position 369 in the naturally occurring channel Kv2.1 also produced fast inactivation. Like N- and C-types of inactivation, pore or P-type inactivation was characterized by short bursts terminated by rapid entry into the inactivated state. Unlike C-type inactivation, in which external tetraethylammonium (TEA) produced a simple blockade that slowed inactivation and reduced currents, in P-type inactivation external TEA increased currents. Unlike N-type inactivation, internal TEA produced a simple reduction in current and K+ occupancy of the pore had no effect. External TEA was not the only cation to increase current; external K+ enhanced channel availability and recovery from inactivation. Additional features of P-type inactivation were residue-specific effects on the extent of inactivation and removal of inactivation by a point reversion at position 374, which also regulates conductance. The demonstration of P-type inactivation indicates that pore residues in K+ channels may be part of the inactivation gating machinery.
De Biasi
M
M
Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, TX 77030.
Hartmann
H A
HA
Drewe
J A
JA
Taglialatela
M
M
Brown
A M
AM
Kirsch
G E
GE
D002678:Chimera / Q000235:genetics / Q000502:physiology; D004274:DNA, Recombinant; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology*; D008564:Membrane Potentials / Q000502:physiology; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000502:physiology; D015221:Potassium Channels / Q000235:genetics / Q000502:physiology*
D004274:DNA, Recombinant; D015221:Potassium Channels