Abstract: | A decrease in nutrient Cl− results in an increased negativity of the nutrient relative to the secretory side. The possibility emerged that Cl− transport could be attributed to a neutral mechanism involving Cl− in the nutrient membrane coupled to a simple Cl− conductance pathway in the secretory membrane. The decrease in PD (potential difference) with a decrease in nutrient Cl− could arise from a decrease in cellular Cl− so that the ratio of Cl− in cell to Cl− in secretory solution was decreased. Experiments were designed to determine whether there was a need to assume a simple Cl− conductance pathway. A 10-fold decrease in Cl− gave in HCO3−-containing nutrient solutions a PD decrease of 20 mV, in HCO3−-free nutrient solutions, a PD decrease of 13.5 mV, and in HCO3−-free and Na+-free solutions, a PD decrease of 6.7 mV. The decrease of 6.7 mV could not be attributed to a neutral Cl−HCO3− exchanger or a NaCl symport. Also there was no evidence for a KCl symport from changes in Cl− in presence and absence of K+. It followed that the decrease of 6.7 mV provided evidence for a simple Cl− conductance pathway in the nutrient membrane. |