Evidence for HCO3- conductance pathways in nutrient membrane of bullfrog antrum

The effect of changing the nutrient HCO3- concentration on potential difference (PD) and resistance in bullfrog antrum bathing in CI- media was determined. Changes in HCO3- concentration were from 25 mM to several lower concentrations and back to 25 mM. A plot of /delta PD/ versus log [HCO3-] gave a linear relation for changes of HCO3- concentration from 25 down to 3.1 mM and back to 25 mM but deviated to some extent for changes to 1.6 mM. In these experiments, changes from higher to lower HCO3- concentrations gave a less rapid initial PD response than those in the reverse direction. This result eliminated H+ conductance pathways as being predominant. Experiments were done in which in the first part changes were made in nutrient solution from 5 percent CO2 and 25 mM HCO3- to 0.6 percent CO2 and 3 mM HCO3- and in the second part the same changes with a simultaneous changes of secretory solution from 5 percent to 10 percent CO2. The magnitude of PD decrease was greater by 4.5 mV in the second part. This result indicated that HCO3- conductance pathways rather than OH- conductance pathways are predominated . There was no evidence of HCO3-, OH-, and H+ conductance pathways in secretory membranes.