EFFECTS OF OLEUROPEOSIDE IN ISOLATED GUINEA-PIG ATRIA

The effects of oleuropeoside were studied on the electromechanical pro perties of isolated guinea-pig atria. In spontaneously beating right a tria, oleuropeoside decreased the amplitude of contractions (IC50 = 1. 3 +/- 0.2 x 10(-4) M), slightly decreased atrial rate, and lengthened sinus node recovery time. Oleuropeoside also inhibited peak contractil e force in electrically driven left atria incubated in normal (IC50 = 1.5 +/- 0.5 x 10(-4) M) and in 27 mM K- Tyrode solution (IC50 = 1. 7 /- 0.4 x 10(-4) M). These negative inotropic effects were not accompan ied by significant changes in the characteristics of action potentials recorded in atria incubated in either normal or depolarizing solution s. These results indicate that oleuropeoside produced an electromechan ical uncoupling that cannot be attributed to an inhibitory effect on C a2+ entry through L-type channels. Therefore, the negative inotropic e ffect may reflect an action of oleuropeoside perhaps at an intracellul ar level.