title: Critical roles of the S3 segment and S3-S4 linker of repeat I in activation of L-type calcium channels.
abstract: Each of the four repeats (or motifs) of voltage-gated ion channels is thought to contain six transmembrane segments (S1-S6). Mutational analyses indicate that S4 functions as a voltage sensor and that the S5, S6, and S5-S6 linker contribute to formation of the ion pore. However, little information exists regarding the functional role(s) of the amino-terminal portion (S1-S3-S4 linker) of the repeats. Here we report that the amino acid composition of the S3 segment of repeat I and the linker connecting S3 and S4 segments of repeat I is critical for the difference in activation kinetics between cardiac and skeletal muscle L-type calcium channels. Mutant dihydropyridine receptors that have the skeletal muscle dihydropyridine receptor sequence in this region activated relatively slowly with the time constant of current activation (tau act) > 5 ms, whereas mutants that have the cardiac counterpart there activated relatively rapidly with tau act < 5 ms. Comparison of these two mutant groups indicates that a total of 11 conservative and 10 nonconservative amino acid changes from skeletal muscle to cardiac dihydropyridine receptor sequence are sufficient to convert activation from slow to fast. These data demonstrate a functional role for this region of voltage-gated ion channels.
authors.affiliation: Department of Medical Chemistry, Kyoto University Faculty of Medicine, Japan.
authors.forename: J
authors.initials: J
authors.lastname: Nakai
authors.forename: B A
authors.initials: BA
authors.lastname: Adams
authors.forename: K
authors.initials: K
authors.lastname: Imoto
authors.forename: K G
authors.initials: KG
authors.lastname: Beam
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015220:Calcium Channels / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D020746:Calcium Channels, L-Type; D002478:Cells, Cultured; D018076:DNA, Complementary / Q000235:genetics; D007700:Kinetics; D051379:Mice; D008969:Molecular Sequence Data; D009124:Muscle Proteins / Q000235:genetics / Q000378:metabolism; D009132:Muscles / Q000378:metabolism; D009154:Mutation; D009206:Myocardium / Q000378:metabolism
chemical_list: D015220:Calcium Channels; D020746:Calcium Channels, L-Type; D018076:DNA, Complementary; D009124:Muscle Proteins