NaCl transport across hen colon. Dependence on electro-chemical driving force

1. Sheets of isolated mucosa from the colon of chickens on either a high or a low NaCl diet were mounted in Ussing chambers. They were bathed in Krebs-phosphate medium and exposed to sodium concentrations ranging from 3.0 to 140 mmol/l (choline-chloride replacement). 2. In the short-circuited state the net fluxes of sodium in the mucosa (m)-serosa (s) direction, followed saturation kinetics with Km = 25 mmol/l in the low-NaCl chickens and 124 mmol/l in the high-NaCl chickens. 3. The unidirectional fluxes of sodium in the s-m direction were linearly related to the electro-chemical driving force. The apparent permeabilities were 8.6 +/- 0.3 x 10(-6) cm/s in the low-NaCl and 11.6 +/- 0.3 x 10(-6) cm/s in the high-NaCl birds. 4. The chloride fluxes were in the short-circuited state of equal magnitude in the m-s and the s-m direction, and in the two dietary states. Changes in the electrical driving force resulted in changes in chloride fluxes compatible with passive flow.