We have established a new model for rat gastric epithelial cell (RGM1) damage caused by both acid and pepsin. Exposure of RGM1 to an acidified medium (pH 3.5-5.0) for 10-50 min decreased cell viability in a time- and pH-dependent manner. Pepsin (0.5-1.0 mg/mL) at pH 4.5 potentiated cell damage in a concentration-dependent manner. Based on these results, two types of cell damage models caused by incubation of cells at pH 4.0 and with pepsin (0.75 mg/mL) at pH 4.5 for 30 min, respectively, were established. The intracellular pH (pHi) gradually decreased with a decrease in medium pH and an increase in exposure time. At pH < or = 4.0, pHi reached approximately pH 6.3. Pepsin at pH 4.5 caused a further reduction in pHi compared with the acidified medium alone. Pepsin pre-incubated with pepstatin did not induce any cell damage. Pretreatment with sucralfate (0.1-3 mg/ mL) for 2 h significantly prevented cell damage caused at both pH 4.0 and with pepsin at pH 4.5 in a concentration-dependent manner. Sucralfate (3 mg/mL) significantly prevented the reduction in pHi at pH 4.0 or with pepsin at pH 4.5. 16,16-Dimethyl prostaglandin E2 (30 micrograms/mL) had no effect on either cell damage or pHi. These cell damage models involving RGM1 are useful for studying the mechanism underlying cell damage and for the screening of cytoprotective drugs.