Melina Möller1, Nicole Silbernagel2, Eva Wrobel1, Birgit Stallmayer3, Elsie Amedonu1,4, Susanne Rinné2, Stefan Peischard1, Sven G Meuth4, Bernhard Wünsch5, Nathalie Strutz-Seebohm1, Niels Decher2, Eric Schulze-Bahr3, Guiscard Seebohm1. 1. Myocellular Electrophysiology and Molecular Biology, Institute for Genetics of Heart Diseases (IfGH), Department of Cardiovascular Medicine, University Hospital Muenster, Muenster, Germany. 2. Institute of Physiology and Pathophysiology, Vegetative Physiology Group, Philipps University of Marburg, Marburg, Germany. 3. Institute for Genetics of Heart Diseases (IfGH), Department of Cardiovascular Medicine, University Hospital Muenster, Muenster, Germany. 4. Department of Neurology, University Hospital Muenster, Muenster, Germany. 5. Institute of Pharmaceutical and Medical Chemistry, University of Muenster, Muenster, Germany.
Abstract
BACKGROUND/AIMS: The hyperpolarization-activated cyclic nucleotide-gated cation channel HCN4 contributes significantly to the generation of basic cardiac electrical activity in the sinus node and is a mediator of modulation by β-adrenergic stimulation. Heterologous expression of sick sinus syndrome (SSS) and bradycardia associated mutations within the human HCN4 gene results in altered channel function. The main aim was to describe the functional characterization of three (two novel and one known) missense mutations of HCN4 identified in families with SSS. METHODS: Here, the two-electrode voltage clamp technique on Xenopus laevis oocytes and confocal imaging on transfected COS7 cells respectively, were used to analyze the functional effects of three HCN4 mutations; R378C, R550H, and E1193Q. Membrane surface expressions of wild type and the mutant channels were assessed by confocal microscopy, chemiluminescence assay, and Western blot in COS7 and HeLa cells. RESULTS: The homomeric mutant channels R550H and E1193Q showed loss of function through increased rates of deactivation and distinctly reduced surface expression in all three homomeric mutant channels. HCN4 channels containing R550H and E1193Q mutant subunits only showed minor effects on the voltage dependence and rates of activation/deactivation. In contrast, homomeric R378C exerted a left-shifted activation curve and slowed activation kinetics. These effects were reduced in heteromeric co-expression of R378C with wild-type (WT) channels. CONCLUSION: Dysfunction of homomeric/heteromeric mutant HCN4-R378C, R550H, and E1193Q channels in the present study was primarily caused by loss of function due to decreased channel surface expression.
BACKGROUND/AIMS: The hyperpolarization-activated cyclic nucleotide-gated cation channel HCN4 contributes significantly to the generation of basic cardiac electrical activity in the sinus node and is a mediator of modulation by β-adrenergic stimulation. Heterologous expression of sick sinus syndrome (SSS) and bradycardia associated mutations within the humanHCN4 gene results in altered channel function. The main aim was to describe the functional characterization of three (two novel and one known) missense mutations of HCN4 identified in families with SSS. METHODS: Here, the two-electrode voltage clamp technique on Xenopus laevis oocytes and confocal imaging on transfected COS7 cells respectively, were used to analyze the functional effects of three HCN4 mutations; R378C, R550H, and E1193Q. Membrane surface expressions of wild type and the mutant channels were assessed by confocal microscopy, chemiluminescence assay, and Western blot in COS7 and HeLa cells. RESULTS: The homomeric mutant channels R550H and E1193Q showed loss of function through increased rates of deactivation and distinctly reduced surface expression in all three homomeric mutant channels. HCN4 channels containing R550H and E1193Q mutant subunits only showed minor effects on the voltage dependence and rates of activation/deactivation. In contrast, homomeric R378C exerted a left-shifted activation curve and slowed activation kinetics. These effects were reduced in heteromeric co-expression of R378C with wild-type (WT) channels. CONCLUSION: Dysfunction of homomeric/heteromeric mutant HCN4-R378C, R550H, and E1193Q channels in the present study was primarily caused by loss of function due to decreased channel surface expression.
Authors: Tengiz Oniani; Laura Vinnenberg; Rahul Chaudhary; Julian A Schreiber; Kathrin Riske; Brandon Williams; Hans-Christian Pape; John A White; Anna Junker; Guiscard Seebohm; Sven G Meuth; Petra Hundehege; Thomas Budde; Mehrnoush Zobeiri Journal: Int J Mol Sci Date: 2022-06-03 Impact factor: 6.208