S-Isopetasin, a sesquiterpene of Petasites formosanus, allosterically antagonized carbachol in isolated guinea pig atria.

Abstract

We investigated the antimuscarinic effect of S-isopetasin in isolated guinea pig atria to clarify whether it preferentially acts on muscarinic M 2 or M 3 receptors. The tension changes of isolated atria were isometrically recorded on a polygraph. S-Isopetasin at 50 and 100 microM significantly inhibited baselines of contractile tension and heart rate, but atropine at 1 microM enhanced both. S-Isopetasin (10 - 100 microM) did not significantly alter the concentration-negative inotropic response curves of carbachol (CCh) in left atria. S-Isopetasin (10 - 100 microM) allosterically antagonized negative inotropic and chronotropic responses induced by CCh in spontaneously beating right atria, based on the slopes of Schild plots significantly differing from unity. On the contrary, atropine (0.01 - 1 microM) competitively antagonized all the above responses to CCh. The pA 2 values of S-isopetasin were significantly less than that of S-isopetasin in guinea pig trachealis, suggesting that S-isopetasin may preferentially act on tracheal muscarinic M 3, but not cardiac muscarinic M 2 receptors. However, atropine preferentially acts neither. This finding reveals that S-isopetasin may have benefit in the treatment of asthma.

• Authors: Wun-Chang Ko, Sheng-Hao Wang, Mei-Chun Chen, Yun-Lian Lin, Chieh-Fu Chen
• Journal: Planta medica (Planta Med) Vol. 68 Issue 7 Pg. 652-5 (Jul 2002) ISSN: 0032-0943 [Print] Germany
• PMID: 12143005 (Publication Type: Letter, Research Support, Non-U.S. Gov't)

Chemical References

• Cardiotonic Agents
• Sesquiterpenes
• Carbachol
• isopetasin

Topics

• Allosteric Regulation
• Animals
• Asteraceae (chemistry)
• Atrial Function
• Carbachol (antagonists & inhibitors)
• Cardiotonic Agents (antagonists & inhibitors)
• Guinea Pigs
• Heart Atria (drug effects)
• Male
• Sesquiterpenes (chemistry, isolation & purification, pharmacology)