Acute cholecystitis develops in gallbladders (GB) with excessive bile cholesterol (Ch). Increased membrane Ch content affects membrane function and may affect PGE₂ receptors involved in the cytoprotection against acute inflammation. This study was aimed at determining whether the cytoprotective response to PGE₂ is affected by lithogenic bile with Ch. Muscle cells from human GB with cholesterol stones (ChS) or pigment stones (PS) were obtained by enzymatic digestion. PGE₂ levels were measured by radioimmunoassay and activities of SOD (superoxide dismutase) and catalase were assayed by spectrophotometry. The contraction in response to H₂O₂ in muscle cells from PS was 14 ± 0.3% not different from normal controls and decreased after the cells were incubated with Ch-rich liposomes (p < 0.05) which increase the Ch content in the plasma membranes. In muscle cells from GB with ChS, H₂O₂ induced contraction was only 9.2 ± 1.3% and increased to 14 ± 0.2% after Ch-free liposomes treatment to remove Ch from the plasma membranes (p < 0.01). H₂O₂ caused a similar increase in the levels of lipid peroxidation and PGE₂ content in muscle cells from GB's with ChS and PS. However, the activities of SOD and catalase were significantly lower in muscle cells from GB's with ChS compared to those with PS. The binding capacity of PGE₂ receptors was also significantly lower in muscle cells from GB's with ChS compared to those with PS. In conclusion, the cytoprotective response to ROS (reactive oxygen species) is reduced in muscle cells from gallbladders with ChS despite of a normal increase in the cellular levels of PGE₂. This impaired cytoprotective response may be due to a dysfunction of PGE₂ receptors with decreased binding capacity resulting from excessive Ch levels in the plasma membrane.