Effects of ouabain on frog gastric mucosa in vitro

The effect of the addition of ouabain to the nutrient solution was determined on resistance, potential difference (p.d.) and H+ secretion rate. In NaCl media, 10(-3) M ouabain decreased significantly the p.d. from 25.6 mV to 16.1 mV in 30 min and to 11.0 mV in 60 min. No significant changes occurred in resistance and H+ secretion rate. In Na2SO4 (Cl(-)-free) media, ouabain produced a biphasic effect on p.d. The p.d. changed from -28.0 mV (nutrient-negative) to a nadir of -37.4 mV in 7 min and then increased to -16.4 mV in 60 min. At the nadir there was no significant change in resistance or H+ secretion rate but at 60 min, unlike Cl- media, resistance increased by 36% and H+ secretion rate decreased by 43%. To decide whether the ouabain-caused decrease in H+ rate in Na2SO4 media was due to an effect on the H+ pump or on resistance of the return pathways, the voltage was clamped at 0 and 40 mV. Clamping the voltage showed that in the case of a marked decrease in the H+ secretion rate, the H+ transport mechanism itself was inhibited (and not the parallel pathway). The decrease in p.d. due to ouabain in Cl- and SO42- media indicates that the (Na+ + K+)-ATPase mechanism may be electrogenic.