[Intracellular activity of Cl- measured with microelectrodes selective for Cl- in superficial epithelial cells of gastric mucosa at "rest"].

Intracellular chloride activity and the electrical membrane potential differences were determined in surface epithelial cells of frog fundic gastric mucosa in resting conditions. Separate measurements were carried out by applying single barreled, (KCl filled), conventional and liquid Cl- -selective microelectrodes. Membrane potentials with respect to the serosal (psi cs) and mucosal surfaces (psi cm) recorded with conventional microelectrodes, were -67 +/- E.S. 1.7 mV and -39.9 mV (as calculated from psi cs and psi T) respectively. The average electrical potential measured with Cl- -selective microelectrodes with respect to the serosal bath (psi Cl-cs) was -30.5 +/- E.S. 1.9 mV which yields an intracellular Cl- activity of 14 mmol/l, a value that is 2.8 times that predicted for an equilibrium distribution across the serosal membrane. On the contrary, Cl- seems to be distributed at equilibrium across the mucosal membrane. These results indicate that Cl- is accumulated across the serosal membrane into gastric cells in an energy requiring step.