title: Functional heterogeneity of the four voltage sensors of a human L-type calcium channel.
abstract: Excitation-evoked Ca(2+) influx is the fastest and most ubiquitous chemical trigger for cellular processes, including neurotransmitter release, muscle contraction, and gene expression. The voltage dependence and timing of Ca(2+) entry are thought to be functions of voltage-gated calcium (CaV) channels composed of a central pore regulated by four nonidentical voltage-sensing domains (VSDs I-IV). Currently, the individual voltage dependence and the contribution to pore opening of each VSD remain largely unknown. Using an optical approach (voltage-clamp fluorometry) to track the movement of the individual voltage sensors, we discovered that the four VSDs of CaV1.2 channels undergo voltage-evoked conformational rearrangements, each exhibiting distinct voltage- and time-dependent properties over a wide range of potentials and kinetics. The voltage dependence and fast kinetic components in the activation of VSDs II and III were compatible with the ionic current properties, suggesting that these voltage sensors are involved in CaV1.2 activation. This view is supported by an obligatory model, in which activation of VSDs II and III is necessary to open the pore. When these data were interpreted in view of an allosteric model, where pore opening is intrinsically independent but biased by VSD activation, VSDs II and III were each found to supply ∼50 meV (∼2 kT), amounting to ∼85% of the total energy, toward stabilizing the open state, with a smaller contribution from VSD I (∼16 meV). VSD IV did not appear to participate in channel opening.
authors.affiliation: Division of Molecular Medicine, Department of Anesthesiology.
authors.forename: Antonios
authors.initials: A
authors.lastname: Pantazis
authors.affiliation: Division of Molecular Medicine, Department of Anesthesiology.
authors.forename: Nicoletta
authors.initials: N
authors.lastname: Savalli
authors.affiliation: dPET, Spokane, WA 99223; and.
authors.forename: Daniel
authors.initials: D
authors.lastname: Sigg
authors.affiliation: Centro Interdisciplinario de Neurociencias de Valparaíso, Facultad de Ciencias, Universidad de Valparaíso, Valparaíso 2360102, Chile.
authors.forename: Alan
authors.initials: A
authors.lastname: Neely
authors.affiliation: Division of Molecular Medicine, Department of Anesthesiology, Department of Physiology, Cardiovascular Research Laboratories, and Brain Research Institute, David Geffen School of Medicine, University of California, Los Angeles, CA 90095; rolcese@ucla.edu.
authors.forename: Riccardo
authors.initials: R
authors.lastname: Olcese
mesh_terms: D000494:Allosteric Regulation; D000595:Amino Acid Sequence; D020746:Calcium Channels, L-Type / Q000737:chemistry / Q000502:physiology*; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D017386:Sequence Homology, Amino Acid
chemical_list: D020746:Calcium Channels, L-Type
keywords: Ca2+ entry; CaV1.2; allostery; fluorometry; gating mechanism