title: Upward movement of IS4 and IIIS4 is a rate-limiting stage in Cav1.2 activation.
abstract: In order to specify the role of individual S4 segments in CaV1.2 gating, charged residues of segments IS4-IVS4 were replaced by glutamine and the corresponding effects on activation/deactivation of calcium channel currents were analysed. Almost all replacements of charges in IS4 and IIIS4 decreased the slope of the Boltzmann curve of channel activation (activation curve) while charge neutralisations in IIS4 and IVS4 did not significantly affect the slope. S4 mutations caused either left or rightward shifts of the activation curve, and in wild-type channels, these S4 mutations hardly affected current kinetics.In slowly gating pore (S6) mutants (G432W, A780T, G1193T or A1503G), neutralisations in S4 segments significantly accelerated current kinetics. Likewise in wild type, charge replacements in IS4 and IIIS4 of pore mutants reduced the slope of the activation curves while substitutions of charges in IIS4 and IVS4 had less or no impact. We propose a gating model where the structurally different S4 segments leave their resting positions not simultaneously. Upward movement of segments IS4 and (to a lesser extend) IIIS4 appear to be a rate-limiting stage for releasing the pore gates. These segments carry most of the effective charge for channel activation. Our study suggests that S4 segments of CaV1.2 control the closed state in domain specific manner while stabilizing the open state in a non-specific manner.
authors: Department of Pharmacology and Toxicology, University of Vienna, Althanstrasse 14, 1090, Vienna, Austria.
authors: Stanislav
authors: S
authors: Beyl
authors: Department of Pharmacology and Toxicology, University of Vienna, Althanstrasse 14, 1090, Vienna, Austria.
authors: Annette
authors: A
authors: Hohaus
authors: Department of Pharmacology and Toxicology, University of Vienna, Althanstrasse 14, 1090, Vienna, Austria.
authors: Stanislav
authors: S
authors: Andranovits
authors: Department of Pharmacology and Toxicology, University of Vienna, Althanstrasse 14, 1090, Vienna, Austria.
authors: Eugen
authors: E
authors: Timin
authors: Department of Pharmacology and Toxicology, University of Vienna, Althanstrasse 14, 1090, Vienna, Austria. steffen.hering@univie.ac.at.
authors: Steffen
authors: S
authors: Hering
mesh_terms: D000200:Action Potentials; D020746:Calcium Channels, L-Type / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D015640:Ion Channel Gating; D009154:Mutation; D000072417:Protein Domains
chemical_list: D020746:Calcium Channels, L-Type; C419385:L-type calcium channel alpha(1C)
keywords: Calcium channel; Electrophysiology; Gating; Heart; Mutational analysis; Patch clamp; Pore; Voltage sensor