Relationship of transmural electrical parameters to the luminal Na concentration in the colon of the fowl (Gallus domesticus).

Electrical parameters: PD, resistance, Isc and amiloride-sensitive-Isc across the fowl colon (in vitro) change in response to the Na content of the diet. On a low-Na diet these changes appear to reflect increases in ion transport, especially amiloride-inhibitable Na transport. In vitro the magnitudes of the changes are related to the Na concentration in the luminal (mucosal) fluid and in birds on a low-Na diet peak at a concentration of about 12.5 mM. Such Na concentrations are similar to those in the colonic fluid of Na-deprived birds. Typical Michaelis-Menten kinetics do not appear to apply, possibly reflecting a local adaptation of the ion transport process in response to its external Na concentration.