title: Cloning and functional characterization of the smooth muscle ether-a-go-go-related gene K+ channel. Potential role of a conserved amino acid substitution in the S4 region.
abstract: The human ether-a-go-go-related gene (HERG) product forms the pore-forming subunit of the delayed rectifier K(+) channel in the heart. Unlike the cardiac isoform, the erg K(+) channels in native smooth muscle demonstrate gating properties consistent with a role in maintaining resting potential. We have cloned the smooth muscle isoform of HERG, denoted as erg1-sm, from human and rabbit colon. erg1-sm is truncated by 101 amino acids in the C terminus due to a single nucleotide deletion in the 14th exon. Sequence alignment against HERG showed a substitution of alanine for valine in the S4 domain. When expressed in Xenopus oocytes, erg1-sm currents had much faster activation and deactivation kinetics compared with HERG. Step depolarization positive to -20 mV consistently produced a transient outward component. The threshold for activation of erg1-sm was -60 mV and steady-state conductance was approximately 10-fold greater than HERG near the resting potential of smooth muscle. Site-directed mutagenesis of alanine to valine in the S4 region of erg1-sm converted many of the properties to that of the cardiac HERG, including shifts in the voltage dependence of activation and slowing of deactivation. These studies define the functional role of a novel isoform of the ether-a-go-go-related gene K(+) channel in smooth muscle.
authors.affiliation: Department of Physiology, University of Oklahoma Health Science Center, Oklahoma City 73104, USA.
authors.forename: Fouzia
authors.initials: F
authors.lastname: Shoeb
authors.forename: Anna P
authors.initials: AP
authors.lastname: Malykhina
authors.forename: Hamid I
authors.initials: HI
authors.lastname: Akbarali
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D015153:Blotting, Western; D003001:Cloning, Molecular; D003106:Colon / Q000378:metabolism; D018076:DNA, Complementary / Q000378:metabolism; D000072237:ERG1 Potassium Channel; D004594:Electrophysiology; D051638:Ether-A-Go-Go Potassium Channels; D005091:Exons; D017353:Gene Deletion; D006801:Humans; D007700:Kinetics; D051379:Mice; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009130:Muscle, Smooth / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000378:metabolism; D016133:Polymerase Chain Reaction; D015221:Potassium Channels / Q000737:chemistry*; D024642:Potassium Channels, Voltage-Gated; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D011817:Rabbits; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D014018:Tissue Distribution; D014981:Xenopus
chemical_list: D018076:DNA, Complementary; D000072237:ERG1 Potassium Channel; D051638:Ether-A-Go-Go Potassium Channels; C000606913:KCNH2 protein, human; C000606915:Kcnh2 protein, mouse; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D020033:Protein Isoforms