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XB-ART-39241
Biochim Biophys Acta 2009 May 01;17885:1138-47. doi: 10.1016/j.bbamem.2009.02.011.
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Associated changes in HCN2 and HCN4 transcripts and I(f) pacemaker current in myocytes.

Zhang Q , Huang A , Lin YC , Yu HG .


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The time- and voltage-dependent inward current generated by the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels contributes to the tissue-specific rhythmic activities in the brain and heart. Four isoforms (HCN1-HCN4) have been identified. Previous studies showed that different HCN isoforms may form functional heteromeric channels. We report here that when HCN2 and HCN4 mRNA were injected into Xenopus oocytes with various ratios of HCN2 over HCN4 at 1:1, 10:1, and 1:10, respectively, the resultant channels showed a depolarized current activation and significantly faster activation kinetics near the midpoint of activation compared with HCN4 homomeric channels. In adult rat myocytes overexpressing HCN4, there was an associated increase in HCN2 mRNA. In neonatal rat myocytes in which HCN2 was knocked down, there was also a simultaneous decrease in HCN4 mRNA. Coimmunoprecipitation experiments showed that HCN2 and HCN4 channel proteins can associate with each other in adult rat ventricles. Finally, in adult myocytes overexpressing HCN4, the hyperpolarization-activated inward current activation, I(f), was shifted to physiological voltages from non-physiological voltages, associated with faster activation kinetics. These data suggested that different ratios of HCN2 and HCN4 transcripts overlapping in different tissues also contribute to the tissue-specific properties of I(f).

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Species referenced: Xenopus laevis
Genes referenced: hcn1 hcn2 hcn4

References [+] :
Altomare, Heteromeric HCN1-HCN4 channels: a comparison with native pacemaker channels from the rabbit sinoatrial node. 2003, Pubmed