Comparative effects of prostaglandin F2alpha and A2 on the cardiac transmembrane potentials

PGF2alpha and PGA1 similarly to PGE1 and PGE2 exerted a dose-dependent dual effect on the maximum rate of depolarization (Vmax) of the cat and guinea-pig left auricle. Low concentrations (0.5 and 1.0 microgram/ml) of PGF2alpha caused a marked increase of Vmax which was proportional to the dose in both species, while the overshoot (OS) remained unchanged. PGF2alpha in a dose of 5 micrometer/ml significantly decreases OS but did not alter Vmax, in a dose of 10 microgram/ml, however, evoked a considerable decrease of Vmax, too. These changes were not related to those in the resting potential (RP). With respect to the repolarization phase no biphasic effect was observed. PGA1 in a dose of 0.02 microgram/ml significantly increased Vmax and RP, too. In the presence of 0.1 microgram/ml of PGA1 Vmax remained unchanged, only a significant hyperpolarizing effect could be observed. A higher concentration (1.0 microgram/ml) of PGA1 evoked a significant decrease of Vmax, without changing RP. The examined concentrations of PGA1 accelerated the initial repolarization (20 and 50% repolarization phase).