Cardiac electrophysiological effects of prostacyclin analogues, 7-oxo-PGI2 and iloprost

The effects of stable prostacyclin (PGI2) analogues, Iloprost (Schering) and 7-oxo-PGI2 (Chinoin) on transmembrane action potential (AP) of guinea pig left auricle and right papillary muscle were studied. 7-oxo-PGI2 (10(-7)-10(-5) M) without causing any significant effect on AP and on the maximum rate of rise (Vmax) of AP accelerated only the repolarization phase at high concentration in both preparations. Iloprost (1.4 x 10(-7)-1.4 x 10(-5) M) had a slight hyperpolarizing effect and it decreased the duration of atrial AP. In ventricular preparation Iloprost depressed the amplitude of the obershoot (OS), shortened the duration of AP and at high concentration (1.4 x 10(-5) M) caused a slight, significant increase in Vmax. Iloprost had no effect on slow AP induced by adrenaline in K+ depolarized ventricular fibers. Some electrophysiological effects of Iloprost can be explained by changing K+ permeability.