Effects of ProstagIand in F2a on the Spontaneous Contractions and Electrical Activities in the Circular Smooth MuscIe of the Guinea-Pig Stomach

= A bs t r ac t = Effects of PGF2a and indomethacin on the mechanical and electrical membrane properties of guinea-pig antral smooth muscle were studied using microeletrodes and tension recording technique and whole cell patch clamp technique. In this tissue, indomethacin inhibited the contractility and such an effect was reversed by PGF2a. PGF2a increased spontaneous contractions potently and the frequency and amplitudes of slow waves were also enhanced. PGF2a-induced contractions were not abolished by the pretreatment with nifedipine o r by the nominal Ca2+-free condition but were abolished by pretreatment with La3+ or absolute Ca2+-free condition. Ionic currents were also measured by whole cell voltage clamp technique. PGF2a increased the size of voltage operated Ca2+ inward currents, and Ca-dependent K+ outward currents, but had no effect on sustained outward currents. From the above results, it is assumed that PGF2a acts as an endogenous prostaglandin in the gastric antrum of the guinea-pig. PGF2a has promoting effects on electrical activities and such effects seem to contribute to the increase of contraction, but the greatest part of the increase of contraction is due to receptor-mediated increase of [Ca2+li. Several possible mechanisms were suggested for the receptor-mediated [Ca2+Ii increase.