THE MECHANISM OF ACTION OF PROSTAGLANDIN F^2α ON THE SMOOTH MUSCLE OF GUINEA-PIG TAENIA COLI

Abstract

The effect of prostaglandin F_2α(PGF_2α) on isolated smooth muscle of guinea-pig taenia coil as related to cholinergic and adrenergic receptors of the muscle was investigated using the double sucrose-gap method. PGF_2α in the concentration of 1.0×10^-6 g/ml caused and augmented the contraction of the smooth muscle by depolarizing the membrane, decreasing the membrane resistance, and increasing the frequency of spike generation. These actions were not abolished by atropine sulfate (10^-7 g/ml), phentolamine (10^-6 g/ml), propranolol (10^-6 g/ml), respectively. PGF_2α had the same action as that of acetylcholine on the contraction of the smooth muscle, but the onset was slower and the duration longer. The inhibitory effects of adrenaline (10^-7 g/ml), noradrenaline (10^-7 g/ml), and isoproterenol (10^-7 g/ml) were not suppressed by treatment with PGF_2α. These results indicate that the effect of PG was not mediated either by the cholinergic nor the adrenergic receptors (α and βreceptors), and it is suggested that PGF_α2 may act on sites of the cell membrane other than adrenergic and cholinergic receptors to increase the membrane conductance as well as in the intracellular mechanism for the induction and augmentation of contraction of the tacnia coli smooth muscle. The interrelationship of the PG and Ca ion is also discussed.