title: Effects of astragaloside IV on action potentials and ionic currents in guinea-pig ventricular myocytes.
abstract: Astragaloside IV (AS-IV) is one of the main active constituents of Astragalus membranaceus, which has various actions on the cardiovascular system. However, its electrophysiological mechanisms are not clear. In the present study, we investigated the effects of AS-IV on action potentials and membrane currents using the whole-cell patch clamp technique in isolated guinea-pig ventricular myocytes. AS-IV prolonged the action potential duration (APD) at all three tested concentrations. The peak effect was achieved with 1×10(-6) M, at which concentration AS-IV significantly prolonged the APD at 95% repolarization from 313.1±38.9 to 785.3±83.7 ms. AS-IV at 1×10(-6) M also enhanced the inward rectifier K(+) currents (I(K1)) and inhibited the delayed rectifier K(+) currents (I(K)). AS-IV (1×10(-6) M) strongly depressed the peak of voltage-dependent Ca(2+) channel current (I(CaL)) from -607.3±37.5 to -321.1±38.3 pA. However, AS-IV was not found to affect the Na(+) currents. Taken together, AS-IV prolonged APD of guinea-pig ventricular myocytes, which might be explained by its inhibition of I(K). AS-IV also influences Ca(2+) signaling through suppressing ICaL.
authors.affiliation: Department of Pharmaceutical Toxicology, School of Pharmaceutical Science, China Medical University, Shenyang, Liaoning 110001, PR China.
authors.forename: Meimi
authors.initials: M
authors.lastname: Zhao
authors.forename: Jinsheng
authors.initials: J
authors.lastname: Zhao
authors.forename: Guilin
authors.initials: G
authors.lastname: He
authors.forename: Xuefei
authors.initials: X
authors.lastname: Sun
authors.forename: Xueshi
authors.initials: X
authors.lastname: Huang
authors.forename: Liying
authors.initials: L
authors.lastname: Hao
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D015220:Calcium Channels / Q000502:physiology*; D004365:Drugs, Chinese Herbal; D006168:Guinea Pigs; D006352:Heart Ventricles / Q000166:cytology; D066298:In Vitro Techniques; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000502:physiology; D015221:Potassium Channels / Q000502:physiology*; D012503:Saponins / Q000494:pharmacology*; D014315:Triterpenes / Q000494:pharmacology*
chemical_list: D015220:Calcium Channels; D004365:Drugs, Chinese Herbal; D015221:Potassium Channels; D012503:Saponins; D014315:Triterpenes; C052064:astragaloside A