[Interactions of PAF and its antagonists in the guinea pig atrial myocardium]

Abstract

The effects of platelet activating factor (PAF) and three its antagonists on the transmembrane intracellular potentials and stimulated (0.5 Hz) contraction amplitude (CA) of the left auricle has been studied. PAF (1-5 X 10(-7) M) was added to the standard Tyrode solution or the same perfusing solution with 15 mM K+, and 6 mM Ca++ (t = 30 degrees C, pH = 7,2). PAF induced the straight cardio-depressing action: the CA always was suppressed during 20 min. The electrical activity was depressed in parallel; in the Tyrode the action potential (AP) duration was lowered, but in the atrial depolarized preparations PAF resulted in a decrease of the slow calcium potential (Ca-AP) amplitude from 100% to 20.2 +/- 2.0%. After 20 min PAF-acting the perfusing solutions contained also one of PAF-antagonists. Antagonist U-66985 led to the weakening of the PAF-depressing effects in the myocardium U-66985 is also able to increase electrical and mechanical activity in myocardium depressed by the blood serum from patients with virulent infections.