Cyclopiazonic Acid Induces Contractions in Ovine Tracheal Smooth Muscle

The aim of this study was to determine the mechanism responsible for the cyclopiazonic acid (CPA)-induced contraction of tracheal smooth muscle. CPA, an inhibitor of Ca2+-ATPase, induced a slowly developing contraction of ovine tracheal strips but had no effect on bronchiolar ring segments. CPA-induced contractions in tracheal strips were abolished in Ca2+-free Krebs solution containing 2 mM EGTA, and were significantly reduced in the presence of verapamil. Influx of 45Ca2+ into the tracheal strips was significantly increased in the presence of CPA. The results suggest that CPA induces contractions of ovine tracheal strips by promoting influx of extracellular Ca2+ through L-type voltage-dependent Ca2+ channels.