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Determinants of activation kinetics in mammalian hyperpolarization‐activated cation channels
Author(s) -
Ishii Takahiro M.,
Takano Makoto,
Ohmori Harunori
Publication year - 2001
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1111/j.1469-7793.2001.0093k.x
Subject(s) - kinetics , transmembrane domain , chemistry , biophysics , hyperpolarization (physics) , linker , gating , patch clamp , pas domain , receptor–ligand kinetics , cyclic nucleotide gated ion channel , cyclic nucleotide binding domain , potassium channel , biochemistry , nucleotide , amino acid , stereochemistry , biology , cyclic nucleotide , nuclear magnetic resonance spectroscopy , transcription factor , receptor , physics , quantum mechanics , computer science , gene , operating system
1 The structural basis for the different activation kinetics of hyperpolarization‐activated cyclic nucleotide‐gated (HCN) channels was investigated with the whole‐cell patch clamp technique by using HCN1, HCN4, chimeric channels and mutants in a mammalian expression system (COS−7). 2 The activation time constant of HCN4 was about 40‐fold longer than that of HCN1 when compared at −100 mV. 3 In chimeras between HCN1 and HCN4, the region of the S1 transmembrane domain and the exoplasmic S1‐S2 linker markedly affected the activation kinetics. The cytoplasmic region between S6 and the cyclic nucleotide‐binding domain (CNBD) also significantly affected the activation kinetics. 4 The S1 domain and S1‐S2 linker of HCN1 differ from those of HCN4 at eight amino acid residues, and each single point mutation of them changed the activation kinetics less than 2‐fold. However, the effects of those mutations were additive and the substitution of the whole S1 and S1‐S2 region of HCN1 by that of HCN4 resulted in a 10− to 20‐fold slowing. 5 The results indicate that S1 and S1‐S2, and S6‐CNBD are the crucial components for the activation gating of HCN channels.