Effects of toosendanin on electric and mechanical properties of guinea pig papillary muscles.
Effects of toosendanin (TS) on the action potentials and contractile force in guinea pig papillary muscles were examined using a standard microelectrode technique. TS concentration-dependently increased the action potential duration at 90% repolarization (APD90) of the fast action potentials. In the presence of a Ikl channel blocker BaCl2, the effects of TS on lengthening the APD90 were completely abolished, thereby suggesting that TS inhibited the inward rectifier K+ current Ikl. The APD and contractile force of aminophylline-induced slow action potentials were potentiated by TS in a concentration-dependent manner. In the presence of BaCl2, both effects of TS were completely abolished. The effect of TS on enhancing contractile force was abolished by the addition of CdCl2, with the prolongation of APD preserved. Thus, TS selectively inhibited the inward rectifier K+ current Ikl with a positive inotropic effect, resulting from a delay in Ca channel inactivation which was secondary to delay in ventricular repolarization.
Gao
X D
XD
Department of Physiology, He-nan Medical University, Zhengzhou, China.
Tang
S B
SB
Lu
J
J
Shi
Y L
YL
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D017609:Barium Compounds / Q000494:pharmacology; D002104:Cadmium / Q000494:pharmacology; D019256:Cadmium Chloride; D002316:Cardiotonic Agents / Q000494:pharmacology*; D002712:Chlorides / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004365:Drugs, Chinese Herbal / Q000494:pharmacology*; D005260:Female; D006168:Guinea Pigs; D008297:Male; D009200:Myocardial Contraction / Q000187:drug effects*; D010210:Papillary Muscles / Q000187:drug effects; D015221:Potassium Channels / Q000187:drug effects; D013268:Stimulation, Chemical; D014315:Triterpenes
D017609:Barium Compounds; D002104:Cadmium; D019256:Cadmium Chloride; D002316:Cardiotonic Agents; D002712:Chlorides; D004365:Drugs, Chinese Herbal; D015221:Potassium Channels; C024986:barium chloride; C036454:toosendanin; D014315:Triterpenes