To characterize further serosal Na uptake into gastric oxyntic cells under resting conditions, cellular element concentrations were determined in isolated frog (Rana temporaria) gastric mucosae using electron microprobe analysis. The epithelia were kept short circuited in Ussing-type chambers, and element analysis was performed on freeze-dried cryosections. After ouabain (10(-4) M), the [Na] in oxyntic cells increased within 30 to 60 minutes from approximately 25 to 100 mmol/kg wet wt, and [K] decreased similarly (from 100 to 25 mmol/kg wet wt). These changes occurred regardless of whether the basolateral incubation medium contained HCO3 or N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) as buffers. When, prior to the addition of ouabain, 10(-3) M amiloride was applied to the serosal side to inhibit the Na-H antiporter, the ouabain-induced increase in cellular [Na] was prevented completely in HEPES-, but not in HCO3-Ringer. The data are compatible with the notion that Na is taken up by a Na-H antiporter and a Na-HCO3 symporter. At least under these experimental conditions, these transporters seem to contribute substantially to basolateral Na uptake in oxyntic cells.