Differences between negative chrono-, dromo- and inotropic actions of cholinomimetics in the dog isolated atrium

Both bethanechol and physostigmine produced dose-dependent negative chrono-, dromo- and inotropic effects in the dog isolated atrial preparation. Within a relatively small dose of bethanechol and physostigmine, negative inotropic effect was clearly induced but no significant chrono- and dromotropic changes were observed. With a relatively large dose, the two cholinomimetics caused negative chrono-, dromo- and inotropic effects. The order of the negative actions of the drugs in % changes was inotropism greater than dromotropism greater than or equal to chronotropism. These results indicate that pacemaker activity, sinoatrial conductivity and atrial contractility may be differentially sensitive to actions of cholinomimetics.