Evidence for electrogenic Na-Cl symport in the in vitro frog stomach.
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.
D000818:Animals; D002712:Chlorides / Q000502:physiology*; D002794:Choline / Q000494:pharmacology; D004594:Electrophysiology; D005071:Evoked Potentials / Q000187:drug effects; D008274:Magnesium / Q000494:pharmacology; D008433:Mathematics; D008564:Membrane Potentials / Q000187:drug effects; D012964:Sodium / Q000502:physiology*; D013270:Stomach / Q000502:physiology*
D002712:Chlorides; D012964:Sodium; D008274:Magnesium; D002794:Choline