title: Mechanism underlying the block of human Cav3.2 T-type Ca2+ channels by benidipine, a dihydropyridine Ca2+ channel blocker.
abstract: OBJECTIVE
  Benidipine, a dihydropyridine Ca(2+) channel blocker, has been reported to block T-type Ca(2+) channels; however, the mechanism underlying this effect was unclear. In this study, we characterized the mechanism responsible for this blocking activity. Furthermore, the blocking activity was compared between two enantiomers of benidipine, (S, S)- and (R, R)-benidipine.
  
  
  METHODS
  Human Ca(v)3.2 (hCa(v)3.2) T-type Ca(2+) channels stably expressed in the human embryonic kidney cell line, HEK-293, were studied in whole-cell patch-clamp recordings and Ca(2+) mobilization assay.
  
  
  RESULTS
  In whole-cell patch-clamp recordings, benidipine blocked hCa(v)3.2 T-type Ca(2+) currents elicited by depolarization to a comparable extent as efonidipine. The block was dependent on stimulation frequency and holding potential, but not test potential. Benidipine significantly shifted the steady-state inactivation curve to the hyperpolarizing direction, but had no effect on the activation curve. Benidipine prolonged the recovery from inactivation of hCa(v)3.2 T-type Ca(2+) channels without any effect on the kinetics of activation, inactivation, or deactivation. In the Ca(2+) mobilization assay, benidipine was more potent than efonidipine in blocking Ca(2+) influx through hCa(v)3.2 T-type Ca(2+) channels. (S, S)-Benidipine was more potent than (R, R)-benidipine in blocking hCa(v)3.2 T-type Ca(2+) currents, but there was no difference in blocking the Ca(2+) influx.
  
  
  CONCLUSIONS
  We have characterized the blocking activity of benidipine against hCa(v)3.2 Ca(2+) channels and revealed the difference between the two enantiomers of benidipine. The blocking action of benidipine could be mediated by stabilizing hCa(v)3.2 Ca(2+) channels in an inactivated state.
authors.affiliation: Toxicological Research Laboratories, Research Division, Kyowa Hakko Kirin Co., Ltd., Shizuoka 411-8731, Japan. atsushi.inayoshi@kyowa-kirin.co.jp
authors.forename: Atsushi
authors.initials: A
authors.lastname: Inayoshi
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Sugimoto
authors.forename: Jun
authors.initials: J
authors.lastname: Funahashi
authors.forename: Saori
authors.initials: S
authors.lastname: Takahashi
authors.forename: Masahiro
authors.initials: M
authors.lastname: Matsubara
authors.forename: Hideaki
authors.initials: H
authors.lastname: Kusaka
mesh_terms: D002121:Calcium Channel Blockers / Q000494:pharmacology*; D020747:Calcium Channels, T-Type / Q000502:physiology*; D004095:Dihydropyridines / Q000494:pharmacology*; D057809:HEK293 Cells; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology
chemical_list: C479952:CACNA1H protein, human; D002121:Calcium Channel Blockers; D020747:Calcium Channels, T-Type; D004095:Dihydropyridines; C061004:benidipine; C038806:1,4-dihydropyridine