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J Clin Invest. 2003 May;111(10):1537-45.

Pacemaker channel dysfunction in a patient with sinus node disease.

Author information

1
Genetics of Arrhythmias, Molecular Cardiology Section, Institute for Arteriosclerosis Research, University of Münster, Münster, Germany. heart@uni-muenster.de

Abstract

The cardiac pacemaker current I(f) is a major determinant of diastolic depolarization in sinus nodal cells and has a key role in heartbeat generation. Therefore, we hypothesized that some forms of "idiopathic" sinus node dysfunction (SND) are related to inherited dysfunctions of cardiac pacemaker ion channels. In a candidate gene approach, a heterozygous 1-bp deletion (1631delC) in exon 5 of the human HCN4 gene was detected in a patient with idiopathic SND. The mutant HCN4 protein (HCN4-573X) had a truncated C-terminus and lacked the cyclic nucleotide-binding domain. COS-7 cells transiently transfected with HCN4-573X cDNA indicated normal intracellular trafficking and membrane integration of HCN4-573X subunits. Patch-clamp experiments showed that HCN4-573X channels mediated I(f)-like currents that were insensitive to increased cellular cAMP levels. Coexpression experiments showed a dominant-negative effect of HCN4-573X subunits on wild-type subunits. These data indicate that the cardiac I(f) channels are functionally expressed but with altered biophysical properties. Taken together, the clinical, genetic, and in vitro data provide a likely explanation for the patient's sinus bradycardia and the chronotropic incompetence.

PMID:
12750403
PMCID:
PMC155041
DOI:
10.1172/JCI16387
[Indexed for MEDLINE]
Free PMC Article

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