Ca2+-agonistic effects of diazepam, a benzodiazepine 1-4 derivative, on isolated mouse and guinea pig left atria

In normal Krebs solution, diazepam (1.75X10(-4) M) increased the action potential duration in a reversible form and caused a positive inotropic effect on mouse auricular muscle (4). 2.) Further studies on diazepam action on electrical and mechanical activity of left auricular muscle from mouse and guinea pig, in preparations electrically driven, showed that diazepam induces an increase in action potential duration measured at 20% repolarization, a decrease in the rate of spike depolarization, and modifies the conduction velocity of the action potential. 3.) Diazepam produced in preparation with spontaneous activity, positive chronotropic and inotropic effects, and positive inotropic effect in electrically driven preparations. 4.) The change in action potential duration induced by diazepam on mouse preparations was higher than on guinea pig preparations, ca.X3. 5.) These findings support that diazepam action may be due to an increase in the inward calcium current and a reduction in the inward sodium current.