The effect of the phenyl phosphonate N-0164 on prostaglandin action and on post inhibitory excitation in the taenia of guinea-pig caecum.

In the taenia of guinea-pig caecum, electrical stimulation of the non-adrenergic inhibitory nerves caused relaxation which was followed by an after-contraction. The purinergic compount ATP (10(-5) M) also produced muscle relaxation while wash-out was associated with an after-contraction. The role of prostaglandins (E1, E2, F1 alpha, F2 alpha; 10(-9)--10(-6 M) in these contractions was studied. The prostaglandin responses reflected by membrane depolarization (E type) and muscle contraction (E and F type) were inhibited by the phenyl phosphonate N-0164 (10(-5) M). This substance did not affect the membrane potential or the nerve-mediated non-adrenergic inhibitory junction potential (IJP). The effect of N-0164 on the muscle cells could account for the limited reduction of the after-depolarization and contraction following electrical stimulation. The ATP after-contraction, however, could be inhibited completely by N-0164. The results are consistent with the possibility that the ATP after-contraction was produced by E type prostaglandins, while involvement of prostaglandins in post inhibitory excitation following nerve stimulation seems unlikely.