Action of Thiamine and Related Compounds on Isolated Clam Heart

1. The action of thiamine and related compounds on the isolated heart of clam (Meretrix meretrix lusoria) was investigated.2. S-benzoylthiamine (SBT) and thiamine propyl disulfide (TPD) among these related compounds displayed a very remarkable positive inotropic action, whereas thiamine, acetylthiamine, thiamine diphosphate, thiamine triphosphate, benzoylthiamine monophosphate and ATP did not practically display any clear action.3. SBT and TPD showed a remarkable antagonistic action against the negative inotropic action of acetylcholine, but have no effect on the action of 5-hydroxytryptamine.4. The positive inotropic action of SBT and TPD was retained in K-free medium, but it completely disappeared in Na-free or Cafree medium. When more or less Na+ or Ca2+ was present in the medium, the action of SBT and TPD appeared as in the normal medium.5. The positive inotropic action of SBT and TPD, therefore, is believed to be closely related to the transport system of the cellular membrane of the clam heart muscle, in which Na+ and Ca2+ are involved.