Effects of tetrandrine on contractility of isolated pig coronary artery strips

Tetrandrine (Tet) 64μM and verapamil (Ver) 8.4 μM relaxed the contraction of coronary artery strips. It is rreversed by raising the extracellular Ca ++ from 2.7 to 14.4μM. within a certain range (Tet 0.1μM-0.1Mm. Ver 1 Nm-1Μm), the % of relaxation was in proportion to dose. However, Tet and Ver exerted no significant inhibition on the extracellular Ca++ contraction induced by NE. It is probable that Tet and Ver primarily inhibited the potential dependent channel (PDC) and prevented the influx of Ca++ through PDC. Tet 10μM and Ver 0.1μM also inhibited the release of intracellular Ca++ by NE. This showed that Tet and Ver might affect the transport of intracellular Ca++. The relaxant effect of Iso on the coronary strips was not blocked by Tet and Ver. Tet is therefore considered to be different from the β-blocker propranolol, but similar to the calcium antagonist Ver.