title: Electrophysiological effect and the gating mechanism of astragaloside IV on L-type Ca(2+) channels of guinea-pig ventricular myocytes.
abstract: Astragaloside IV (AS-IV) is one of the main active ingredients of Astragalus membranaceus. This study is aimed to investigate AS-IV׳s effects on Ca(2+) channel activity of single cardiomyocytes and single Ca(2+) channels. Whole-cell Ca(2+) currents in freshly dissociated cardiomyocytes were measured using the whole-cell patch-clamp technique. Single Ca(2+) channel currents were examined in cell-attached patches and inside-out patches. In the whole-cell recording, AS-IV reduced the amplitude of L-type Ca(2+) currents (ICaL) in a concentration-dependent manner. Although AS-IV did not alter the steady-state activation curves, the voltage dependence of the current inactivation curves was negatively shifted by AS-IV in a concentration dependent manner. Consistent with the results of the whole-cell recording, in the inside-out configuration the ensemble average of single Ba(2+) current via L-type Ca(2+) channel was dose-dependently reduced by AS-IV. The reduction of unitary Ba(2+) current at 0.1 or 1 µM AS-IV was accounted for a decrease in the channel activity (NPo). In addition to the decrease in NPo, there was a reduction of Po without a change in channel number or an apparent change in single channel current. Furthermore, we found that the open-closed kinetics of the channel were affected by AS-IV. AS-IV induced the shift of L-type Ca(2+) channels from either brief openings (mode 1) or long-lasting openings (mode 2) to no active opening (mode 0). Our results suggest that AS-IV blocks the currents through Ca(2+) channels in guinea-pig ventricular myocytes by affecting the open-closed kinetics of L-type Ca(2+) channels to inhibit the channel activities. This study could provide theoretical basis for the drug exploiting of the monomer of Astragalus membranaceus.
authors.affiliation: Department of Pharmaceutical Toxicology, School of Pharmacy, China Medical University, Shenyang 110001, China; Cardiovascular Institute of China Medical University, Shenyang 110001, China.
authors.forename: Meimi
authors.initials: M
authors.lastname: Zhao
authors.affiliation: Department of Pharmaceutical Toxicology, School of Pharmacy, China Medical University, Shenyang 110001, China.
authors.forename: Dongxue
authors.initials: D
authors.lastname: Shao
authors.affiliation: Department of Pharmaceutical Toxicology, School of Pharmacy, China Medical University, Shenyang 110001, China.
authors.forename: Lifeng
authors.initials: L
authors.lastname: Yu
authors.affiliation: Department of Pharmaceutical Toxicology, School of Pharmacy, China Medical University, Shenyang 110001, China.
authors.forename: Xuefei
authors.initials: X
authors.lastname: Sun
authors.affiliation: Department of Pharmaceutical Toxicology, School of Pharmacy, China Medical University, Shenyang 110001, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Department of Pharmaceutical Toxicology, School of Pharmacy, China Medical University, Shenyang 110001, China.
authors.forename: Huiyuan
authors.initials: H
authors.lastname: Hu
authors.affiliation: Department of Pharmaceutical Toxicology, School of Pharmacy, China Medical University, Shenyang 110001, China.
authors.forename: Rui
authors.initials: R
authors.lastname: Feng
authors.affiliation: Department of Pharmaceutical Toxicology, School of Pharmacy, China Medical University, Shenyang 110001, China.
authors.forename: Qinghua
authors.initials: Q
authors.lastname: Gao
authors.affiliation: Department of Pharmaceutical Toxicology, School of Pharmacy, China Medical University, Shenyang 110001, China.
authors.forename: Feng
authors.initials: F
authors.lastname: Guo
authors.affiliation: Department of Pharmaceutical Toxicology, School of Pharmacy, China Medical University, Shenyang 110001, China; Cardiovascular Institute of China Medical University, Shenyang 110001, China. Electronic address: lyhao@mail.cmu.edu.cn.
authors.forename: Liying
authors.initials: L
authors.lastname: Hao
mesh_terms: D000818:Animals; D020746:Calcium Channels, L-Type / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004365:Drugs, Chinese Herbal / Q000494:pharmacology*; D055724:Electrophysiological Phenomena / Q000187:drug effects / Q000502:physiology; D006168:Guinea Pigs; D006352:Heart Ventricles / Q000166:cytology / Q000187:drug effects; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000502:physiology*; D012503:Saponins / Q000494:pharmacology*; D014315:Triterpenes / Q000494:pharmacology*
chemical_list: D020746:Calcium Channels, L-Type; D004365:Drugs, Chinese Herbal; D012503:Saponins; D014315:Triterpenes; C052064:astragaloside A
keywords: AS-IV; Patch-clamp; l-type Ca(2+) channel