Activity of Chloride in Absorptive Cells of Amphiuma Small Intestine

Double-barreled chloride-selective microelectrodes constructed by a new method have been used to determine intracellular chloride activity (aic1) in the absorptive cells of isolated, stripped proximal and distal segments of Amphiuma small intestine. Chloride was passively distributed across the mucosal membrane in fall and winter animals and aic1 is about 20 mM. In contrast summer animals actively accumulated chloride in both proximal and distal segments. Parallel measurements of intracellular chloride concentration (Cic1) reveal a very low apparent chloride activity coefficient (aic1/CiC1) indicating that all of the chloride is not free in the cytoplasm. The chloride activity in the bath immediately adjacent to the mucosa is higher than in the bulk solution.