Effects of prostaglandin E2 (PGE2) on exocytosis of mucin were studied in mucous cells isolated from guinea-pig antrum using video-microscopy. Stimulation with PGE2 elicited a sustained increase in the frequency of exocytotic events in a dose-dependent manner, which was under regulation by both Ca2+ and cAMP. Stimulation with a selective prostanoid EP4 receptor agonist (ONO-AEI-329, 10 µM), which activates cAMP signals, elicited a sustained increase in the frequency of exocytotic events (30 % of that evoked by 1 µM PGE2). Stimulation with an EP1 agonist (17-P-T-PGE2, 1 µM), which activates Ca2+ signals, increased the frequency of exocytotic events to a lesser extent (5 % of that evoked by 1 µM PGE2), while addition of an EP1 antagonist (ONO-8713, 10 µM) decreased the frequency of exocytotic events (approximately 40 % of that evoked by 1 µM PGE2). However, addition of the EP1 agonist potentiated the frequency of exocytotic events evoked by the EP4 agonist or forskolin (which elevates cAMP levels) and increased the sensitivity of the exocytotic events to forskolin. These results suggest that the Ca2+ signal activated via the EP1 receptor potentiates the cAMP-regulated exocytotic events activated via the EP4 receptor during PGE2 stimulation, by increasing the sensitivity of the exocytotic response to cAMP. In conclusion, exocytotic events in PGE2-stimulated antral mucous cells were regulated by interactions between EP1 and EP4 receptors. Experimental Physiology (2001) 86.4, 451-460.