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Voltage clamping across the frog gastric mucosa, nutrient positive to secretory, results in an increase in the open-circuit potential difference (OCPD). The increase in OCPD, or polarization, induced by voltage clamping could be caused by a redistribution of ions across the plasma membrane or by a polarization of pump electromotive forces, such as the Na(+)-K(+)-adenosinetriphosphatase (ATPase) located in the nutrient (serosal) membrane or the proton pump located in the secretory (luminal) membrane. The polarization induced by voltage clamping was not affected by removing Cl- and Na+ or by increasing the K+ concentration to 79 mM but was markedly reduced by placing in the nutrient solution 10(-3) M famotidine or 10(-4) M omeprazole. These data suggest that there is a strong contribution of the proton pump to the polarization induced by voltage clamping with some contribution of ion redistribution and/or the Na(+)-K(+)-ATPase. The data support the electrogenicity of the proton pump.

The transmucosal potential difference (PD) response to step changes in Na+ (choline or Mg2+ for Na+) in the nutrient fluid was studied. Decreasing the Na+ concentration in the nutrient fluid decreased the positivity of the nutrient side, and increasing the Na+ concentration increased the positivity. This effect is anomalous because it is opposite to that of a simple Na+ conductive pathway but right for a choline or Mg2+ conductive pathway. The lack of linearity of delta PD versus the log of the choline concentration ruled out a choline conductive pathway. An approximate linear relation was obtained for Na+. The anomalous PD response for Na+ was reduced but not abolished in 1) K+-free bathing fluids and 2) 10(-3) M ouabain in nutrient fluid. Changing the Cl- concentration in nutrient fluid gave normal PD responses, which were reduced in the absence of Na+. These results are attributed to a passive electrogenic Na-Cl symport. Theoretical considerations, for p Na+ and q Cl- transported per cycle (with q greater than p), predict an anomalous delta PD for Na+ concentration changes and a normal delta PD for Cl- concentration changes.