AJP - Gastrointestinal and Liver Physiology, Vol 242, Issue 6 620-G627, Copyright © 1982 by American Physiological Society
Evidence for electrogenic Na-Cl symport in the in vitro frog stomach
G. Carrasquer, T. C. Chu, W. S. Rehm and M. Schwartz
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.
