Iloprost: Intracellular Ca2+-dependent Contractile Effect on Isolated Smooth Muscle Cells from Guinea-pig Ileum

Prostaglandin E 2 (PGE 2 ) and iloprost induced a concentration-dependent contraction of smooth muscle cells isolated from the circular layer of guinea-pig ileum. PGE 2 - and iloprost-induced contractions were inhibited by the selective EP 1 -receptor antagonist, SC19220 (1-acetyl-2-(8-chloro-10, 11-dihydrodibenz (b,f) (1,4) oxazepine-10-carbonyl)-hydrazine), indicating the involvement of the EP 1 subtype of the PGE 2 receptor. When cells were incubated for 10 min in the presence of strontium (4 mM L -1 ), an inhibitor of the release of Ca 2+ from intracellular store, the contractile effect of PGE 2 and iloprost was inhibited. In contrast, incubation of cells in Ca 2+ -free medium, Ca 2+ -free medium plus EGTA, or in the presence of nifedipine, an organic Ca 2+ -channel blocker, did not alter the PGE 2 - and iloprost-induced contraction. These observations suggest that the myogenic effect of PGE 2 and iloprost on intestinal smooth muscle is dependent on the release of intracellular calcium.