title: Contrasting the roles of the I-II loop gating brake in CaV3.1 and CaV3.3 calcium channels.
abstract: Low-voltage-activated CaV3 channels are distinguished among other voltage-activated calcium channels by the most negative voltage activation threshold. The voltage dependence of current activation is virtually identical in all three CaV3 channels while the current kinetics of the CaV3.3 current is one order slower than that of the CaV3.1 and CaV3.2 channels. We have analyzed the voltage dependence and kinetics of charge (Q) movement in human recombinant CaV3.3 and CaV3.1 channels. The voltage dependence of voltage sensor activation (Qon-V) of the CaV3.3 channel was significantly shifted with respect to that of the CaV3.1 channel by +18.6 mV and the kinetic of Qon activation in the CaV3.3 channel was significantly slower than that of the CaV3.1 channel. Removal of the gating brake in the intracellular loop connecting repeats I and II in the CaV3.3 channel in the ID12 mutant channel shifted the Qon-V relation to a value even more negative than that for the CaV3.1 channel. The kinetic of Qon activation was not significantly different between ID12 and CaV3.1 channels. Deletion of the gating brake in the CaV3.1 channel resulted in a GD12 channel with the voltage dependence of the gating current activation significantly shifted toward more negative potentials. The Qon kinetic was not significantly altered. ID12 and GD12 mutants did not differ significantly in voltage dependence nor in the kinetic of voltage sensor activation. In conclusion, the putative gating brake in the intracellular loop connecting repeats I and II controls the gating current of the CaV3 channels. We suggest that activation of the voltage sensor in domain I is limiting both the voltage dependence and the kinetics of CaV3 channel activation.
authors: Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Vlarska 5, 833 34, Bratislava, Slovakia.
authors: Mária
authors: M
authors: Karmažínová
authors: Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Vlarska 5, 833 34, Bratislava, Slovakia.
authors: Katarína
authors: K
authors: Jašková
authors: Institute of Animal Biochemistry and Genetics, Slovak Academy of Sciences, Ivanka pri Dunaji, Slovakia.
authors: Peter
authors: P
authors: Griac
authors: Department of Pharmacology, University of Virginia, Charlottesville, VA, 22908, USA.
authors: Edward
authors: E
authors: Perez-Reyes
authors: Institute of Molecular Physiology and Genetics, Slovak Academy of Sciences, Vlarska 5, 833 34, Bratislava, Slovakia. lubica.lacinova@savba.sk.
authors: Ľubica
authors: Ľ
authors: Lacinová
mesh_terms: D020747:Calcium Channels, T-Type / Q000737:chemistry / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D015640:Ion Channel Gating; D017434:Protein Structure, Tertiary
chemical_list: C121855:CACNA1G protein, human; C469757:CACNA1I protein, human; D020747:Calcium Channels, T-Type
keywords: Activation kinetic; CaV3.1; CaV3.3; Gating current; T-type calcium channels