A Gastric Housekeeping Cl− Channel Activated via Prostaglandin EP3 Receptor-mediated Ca2+/Nitric Oxide/cGMP Pathway

Prostaglandin E2 (PGE2) has a cytoprotective role in the gastric parietal cell. PGE2 opened a housekeeping basolateral Cl- channel of rabbit gastric parietal cells, the single channel conductance of which was about 0.3 picosiemens. In the present patch-clamp and Fura 2 fluorescence studies, we found that PGE2 increased the intracellular free Ca2+ concentration ([Ca2+]i) and that PGE2-induced opening of the Cl- channel depended on the increase of [Ca2+]i. A novel bifunctional prostaglandin EP3 agonist/EP1 antagonist, 5(Z)-7-[1S, 2S, 3S, 5R)-3-(trans-beta-styren) sulfonamido-6,6-dimethylbicyclo- (3.1.1)hept-2-yl]-5-heptenoic acid, also increased both [Ca2+]i and channel opening. The PGE2-induced effect was mediated via production of nitric oxide (NO); that is, NG-monomethyl-L-arginine, an inhibitor of NO production, markedly inhibited the PGE2-induced channel opening, and nitroprusside, a NO donor, induced the channel opening in the absence of PGE2. Both PGE2 and A23187, Ca2+ ionophore, elevated the cGMP content of isolated parietal cells. The A23187-induced channel opening was abolished by methylene blue, a guanylate cyclase inhibitor. In conclusion, we found that the PGE2-induced opening of the housekeeping Cl- channel in the parietal cell involves the EP3 receptor-mediated increase in [Ca2+]i via a pertussis toxin-sensitive GTP-binding protein, resulting in successive production of NO and cGMP.