Iloprost: intracellular Ca(2+)-dependent contractile effect on isolated smooth muscle cells from guinea-pig ileum

Prostaglandin E2 (PGE2) and iloprost induced a concentration-dependent contraction of smooth muscle cells isolated from the circular layer of guinea-pig ileum. PGE2- and iloprost-induced contractions were inhibited by the selective EP1-receptor antagonist, SC19220 (1-acetyl-2-(8-chloro-10, 11-dihydrodibenz (b,f) (1,4) oxazepine-10-carbonyl)-hydrazine), indicating the involvement of the EP1 subtype of the PGE2 receptor. When cells were incubated for 10 min in the presence of strontium (4 mM L-1), an inhibitor of the release of Ca2+ from intracellular store, the contractile effect of PGE2 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 PGE2- and iloprost-induced contraction. These observations suggest that the myogenic effect of PGE2 and iloprost on intestinal smooth muscle is dependent on the release of intracellular calcium.