Aim: To study effects of arachidonic acid (AA) and its metabolites on the hyposmotic membrane stretch-induced increase in calcium-activated potassium currents (IKCa) in gastric myocytes. Methods: Membrane currents were recorded by using a conventional whole cell patch-clamp technique in gastric myocytes isolated with collagenase. Results: Hyposmotic membrane stretch and AA increased both IK(Ca) and spontaneous transient outward currents significantly.Exogenous AA could potentiate the hyposmotic membrane stretch-induced increase in IK(Ca). The hyposmotic membrane stretch-induced increase in IK(Ca) was significantly suppressed by dimethyleicosadienoic acid (100 μmol/L in pipette solution), an inhibitor of phospholipase A2. Nordihydroguaiaretic acid, a lipoxygenase inhibitor, significantly suppressed AA and hyposmotic membrane stretch-induced increases in IK(Ca). Exteal calcium-free or gadolinium chloride, a blocker of stretch-activated channels, blocked the AA-induced increase in IK(Ca) significantly, but it was not blocked by nicardipine, an L-type calcium channel blocker. Ryanodine, a calcium-induced calcium release agonist, completely blocked the AA-induced increase in IK(Ca); however, heparin, a potent inhibitor of inositol triphosphate receptor, did not block the AA-induced increase in IK(Ca). Conclusion:Hyposmotic membrane stretch may activate phospholipase A2, which hydrolyzes membrane phospholipids to ultimately produce AA; AA as a second messenger mediates Ca2+ influx, which triggers Ca2+-induced Ca2+ release and elicits activation of IK(Ca) in gastric antral circular myocytes of the guinea pig.