184 ELECTROLYTES IN BIOLOGICAL SYSTEMS 



conductance. Those ions actively transported will have asymmetrical fluxes, 

 and the net fluxes should be algebraically summed to explain the mucosal cur- 

 rent. Additional confirmation will be needed from flux rates at several mucosal 

 potentials to clarify the extent to which each ion actually moves by passive 

 diffusion or alternatively passes by exchange diffusion. 



Sodium fluxes across the short-circuited isolated mucosa are symmetrical, 

 and if the movement were entirely passive would account for about 25% of the 

 total membrane conductance (48). When there is a potential difference across 

 the mucosa, the flux ratio is less than that theoretically predicted for purely 

 passive diffusion. Though this deviation may, in part, be due to experimental 

 technique, the departure of the observed from the theoretical is consistent with 

 at least 80% of the sodium movement being one of passive diffusion. A less 

 thorough study of potassium flux did not demonstrate a significant flux asym- 



Table I. Chloride transfer by short-circuited isolated mucosa (r. catesbiana); 



flEQ. CM~^ HR."' 



NET CHLORIDE TRANSFER NET CHARGE TRANSFER 



Flux N - S 10.65 Current 3.05 



Flux S - N 6.38 H''' secretion 1.20 



4.27 4.25 



Mean conductivity: - Start 3.21 m.mhos 

 End 2.28 m.mhos 



Experimental demonstration that net chloride tiux is equal to the sum of the mucosal 

 short-circuit current and hydrogen ion secretion. The net chloride flux is the difference be- 

 tween the nutrient to secretory flux (Flux N — S) and the secretory to nutrient flux (Flux 



S - N). 



metry at o mv. At 56 mv the fluxes were significantly asymmetrical as expected 

 for a passive ion. In absolute values the potassium fluxes were | of those of 

 sodium, though the K/Na concentration of the bathing solutions was 2.5/1 15, 

 and, at most, potassium would account for only another 5% of the total mem- 

 brane conductance (48). 



Chloride transfer across the gastric epithelium departs markedly from that 

 expected of a passive ion. Chloride is actively transported and the absolute 

 values of its fluxes is unexpectedly large. Table i is a summary of the chloride 

 flux data obtained during 48 one-hour periods from 8 gastric mucosae. Each 

 mucosa was divided into halves, each half being used to measure either one or 

 the other flux. In order to avoid a confusion which comes from speaking of the 

 lumen of the stomach as the outside, the following convention will be observed 

 in this paper when speaking of the fluxes and surfaces of the stomach. The 

 nutrient to secretory (X — > S) flux is the unidirectional movement from the 



