Sanguinarine: A positive inotropic alkaloid which inhibits cardiac Na +,K +-ATPase

In isolated, isometrically contracting left guinea pig atria, sanguinarine, a benzophenanthridine alkaloid from the papaveracea Sanguinaria canadensis, produced a concentration-dependent positive inotropic effect. Between 2.3 × 10 −6 M and 6.5 × 10 −5 M, sanguinarine increased contractility by 108% which was comparable to the maximal inotropic effect of ouabain. Within the same concentration range, sanguinarine caused inhibition of Na +,K +-ATPase isolated from guinea pig myocardium. 100% inhibition of Na +,K +-ATPase activity occurred at 1 × 10 −4 M sanguinarine. The I 50 for enzyme inhibition and the ED 50 for the inotropic action of sanguinarine were the same (6–6.5 × 10 −6 M) indicating that both effects may be causally related.