Comparison of the effects of a benzotriazinium iodide and quinidine on guinea-pig heart

The actions of 2-n-propyl-4-p-tolylamino-1,2,3-benzotriazinium iodide (TnPBI) and quinidine were compared on guinea-pig heart preparations. Quinidine had negative inotropic and chronotropic effects on guinea-pig isolated atria and on Langendorff hearts: TnPBI had negative inotropic and chronotropic effects on Langendorff hearts, but showed a positive inotropic effect on isolated atria at low dose levels. Both quinidine and TnPBI increased the effective refractory period of guinea-pig atrial preparations. The effects of TnPBI on transmembrane action potentials indicated a mixed class I and class III action according to the classification of Vaughan Williams (1970). These effects are discussed in relation to the antiarrhythmic actions of TnPBI.