title: K+ channel regulator KCR1 suppresses heart rhythm by modulating the pacemaker current If.
abstract: Hyperpolarization-activated, cyclic nucleotide sensitive (HCN) channels underlie the pacemaker current I(f), which plays an essential role in spontaneous cardiac activity. HCN channel subunits (HCN1-4) are believed to be modulated by additional regulatory proteins, which still have to be identified. Using biochemistry, molecularbiology and electrophysiology methods we demonstrate a protein-protein interaction between HCN2 and the K(+) channel regulator protein 1, named KCR1. In coimmunoprecipitation experiments we show that KCR1 and HCN2 proteins are able to associate. Heterologously expressed HCN2 whole-cell current density was significantly decreased by KCR1. KCR1 profoundly suppressed I(HCN2) single-channel activity, indicating a functional interaction between KCR1 and the HCN2 channel subunit. Endogenous KCR1 expression could be detected in adult and neonatal rat ventriculocytes. Adenoviral-mediated overexpression of KCR1 in rat cardiomyocytes (i) reduced I(f) whole-cell currents, (ii) suppressed most single-channel gating parameters, (iii) altered the activation kinetics, (iv) suppressed spontaneous action potential activity, and (v) the beating rate. More importantly, siRNA-based knock-down of endogenous KCR1 increased the native I(f) current size and single-channel activity and accelerated spontaneous beating rate, supporting an inhibitory action of endogenous KCR1 on native I(f). Our observations demonstrate for the first time that KCR1 modulates I(HCN2)/I(f) channel gating and indicate that KCR1 serves as a regulator of cardiac automaticity.
authors.affiliation: Department of Internal Medicine III, University of Cologne, Cologne, Germany.
authors.forename: Guido
authors.initials: G
authors.lastname: Michels
authors.forename: Fikret
authors.initials: F
authors.lastname: Er
authors.forename: Ismail F
authors.initials: IF
authors.lastname: Khan
authors.forename: Jeannette
authors.initials: J
authors.lastname: Endres-Becker
authors.forename: Mathias C
authors.initials: MC
authors.lastname: Brandt
authors.forename: Natig
authors.initials: N
authors.lastname: Gassanov
authors.forename: David C
authors.initials: DC
authors.lastname: Johns
authors.forename: Uta C
authors.initials: UC
authors.lastname: Hoppe
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D001283:Atrioventricular Node / Q000378:metabolism; D001683:Biological Clocks; D002478:Cells, Cultured; D017931:DNA Primers; D047468:Immunoprecipitation; D015640:Ion Channel Gating; D009200:Myocardial Contraction / Q000502:physiology*; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000502:physiology*; D015221:Potassium Channels / Q000235:genetics / Q000502:physiology*; D034741:RNA, Small Interfering; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection
chemical_list: C114599:Alg10 protein, rat; D017931:DNA Primers; D009419:Nerve Tissue Proteins; D015221:Potassium Channels; D034741:RNA, Small Interfering