title: Two mechanistically distinct effects of dihydropyridine nifedipine on CaV1.2 L-type Ca²⁺ channels revealed by Timothy syndrome mutation.
abstract: Dihydropyridine Ca(2+) channel antagonists (DHPs) block Ca(V)1.2 L-type Ca(2+) channels (LTCCs) by stabilizing their voltage-dependent inactivation (VDI); however, it is still not clear how DHPs allosterically interact with the kinetically distinct (fast and slow) VDI. Thus, we analyzed the effect of a prototypical DHP, nifedipine on LTCCs with or without the Timothy syndrome mutation that resides in the I-II linker (L(I)-(II)) of Ca(V)1.2 subunits and impairs VDI. Whole-cell Ba(2+) currents mediated by rabbit Ca(V)1.2 with or without the Timothy mutation (G436R) (analogous to the human G406R mutation) were analyzed in the presence and absence of nifedipine. In the absence of nifedipine, the mutation significantly impaired fast closed- and open-state VDI (CSI and OSI) at -40 and 0 mV, respectively, but did not affect channels' kinetics at -100 mV. Nifedipine equipotently blocked these channels at -80 mV. In wild-type LTCCs, nifedipine promoted fast CSI and OSI at -40 and 0 mV and promoted or stabilized slow CSI at -40 and -100 mV, respectively. In LTCCs with the mutation, nifedipine resumed the impaired fast CSI and OSI at -40 and 0 mV, respectively, and had the same effect on slow CSI as in wild-type LTCCs. Therefore, nifedipine has two mechanistically distinct effects on LTCCs: the promotion of fast CSI/OSI caused by L(I-II) at potentials positive to the sub-threshold potential and the promotion or stabilization of slow CSI caused by different mechanisms at potentials negative to the sub-threshold potential.
authors.affiliation: Department of Molecular Pharmacology, Shinshu University School of Medicine, Matsumoto, Nagano, Japan.
authors.forename: Xiaona
authors.initials: X
authors.lastname: Sheng
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Nakada
authors.forename: Motohiro
authors.initials: M
authors.lastname: Kobayashi
authors.forename: Toshihide
authors.initials: T
authors.lastname: Kashihara
authors.forename: Toshihide
authors.initials: T
authors.lastname: Shibazaki
authors.forename: Miwa
authors.initials: M
authors.lastname: Horiuchi-Hirose
authors.forename: Simmon
authors.initials: S
authors.lastname: Gomi
authors.forename: Masamichi
authors.initials: M
authors.lastname: Hirose
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Aoyama
authors.forename: Mitsuhiko
authors.initials: M
authors.lastname: Yamada
mesh_terms: D000494:Allosteric Regulation; D000818:Animals; D001321:Autistic Disorder; D002121:Calcium Channel Blockers / Q000494:pharmacology*; D020746:Calcium Channels, L-Type / Q000187:drug effects* / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D008133:Long QT Syndrome / Q000235:genetics*; D008564:Membrane Potentials; D009154:Mutation; D009543:Nifedipine / Q000494:pharmacology*; D011817:Rabbits; D051381:Rats; D013576:Syndactyly / Q000235:genetics*
chemical_list: D002121:Calcium Channel Blockers; D020746:Calcium Channels, L-Type; D009543:Nifedipine