Effects of ciguatoxin and maitotoxin on the isolated guinea pig atria

The effects of ciguatoxin (CT) and maitotoxin (MT) were studied on the isolated atria of the guinea pig. Application of CT evoked a prolonged positive inotropic effect on the electrically-driven atria and both inotropic and chronotropic effects on the spontaneously-beating right atria. The response to MT in contrast was biphasic. At low concentration (10(-8) Gm per ml) MT enhanced the atrial contractility, while at higher concentrations (5 x 10(-8) Gm per ml) it depressed the atria and frequently to a standstill. The results indicate that CT and MT have a direct action on the contractile mechanism of the heart and their effects are readily distinguishable.