Contractile effects of vanadate on monkey and rabbit tracheal smooth muscle

The effects of vanadate (Na3VO4: VAN) on isolated tracheal smooth muscle of monkey (Macaca fascicularis) and rabbit were examined. VAN (10(-5)-10(-3) M) induced a sustained contraction in both tracheae which was not affected by atropine, tetrodotoxin or tripelennamine. Indomethacin potentiated VAN-induced contraction in monkey trachea but had no effect in rabbit trachea. In Ca-free solution, high K was ineffective whereas VAN or carbachol induced a small transient contraction. In both tracheae, the K-induced contraction was completely inhibited by verapamil while the VAN- and carbachol-induced contractions were partially inhibited by this inhibitor. Sodium nitroprusside was ineffective in rabbit trachea. In monkey trachea, however, K-induced contraction was completely inhibited and VAN- and carbachol-induced contractions were partially inhibited by sodium nitroprusside. Readmission of 5.4 mM K transiently relaxed the carbachol-induced contraction in trachea pretreated with a K-free solution. Ouabain completely and VAN partially inhibited this K-induced relaxation. VAN slightly increased the cellular Na content in rabbit trachea but not in monkey trachea. Previous inhibition of the Na pump activity by a K-free solution containing ouabain did not inhibit the VAN-induced contraction. It is concluded that VAN induces a transient, followed by a sustained contraction in both monkey and rabbit tracheae. The former contraction may be due to a release of cellular Ca and the latter to an influx of external Ca. VAN-induced contractions do not seem to be due to an inhibition of the Na pump activity.