The effects of gaseous hypoxia and reoxygenation on oxynticopeptic (OPC) and surface mucous cells (SMC) were examined in in vitro bullfrog gastric fundic mucosae mounted in Ussing chambers. Forskolin-stimulated H+ secretion, transmucosal potential difference (PD), and electrical resistance (R) were monitored in tissues incubated in HCO3(-)-free or HCO3(-)-containing buffer. At serosal pH (pHs) 7.2, 1 h of hypoxia with 100% N2 resulted in a decrease in PD, increase in R, and complete inhibition of H+ secretion. After 30 min of hypoxia, the morphology of OPC changed from the secretory to the nonsecretory state without recognizable cytopathology. Destructive changes in OPC increased progressively at pHs 7.2 as the hypoxic period was prolonged from 4 to 24 h. After 4 h of reoxygenation following 12-24 h of hypoxia, OPC remained necrotic and H+ secretion showed no recovery, whereas in some areas where SMC were exfoliated adjacent SMC showed epithelial restitution. The recovery of H+ secretion and PD during 2 h of reoxygenation after 4 h of hypoxia at pHs 6.0 and 6.8 was less than that at 7.2 and 8.0 and was greater in the presence of serosal HCO3- than its absence at pHs 7.2. These results suggest that, in in vitro frog gastric mucosa, 1) OPC are more vulnerable to hypoxia than SMC, 2) basolateral acidosis exaggerates hypoxic injury of OPC, and 3) serosal HCO3- protects OPC from hypoxic injury.