Mechanism of Cl secretion in canine trachea: changes in intracellular chloride activity with secretion.

Cl-sensitive microelectrodes were employed to investigate the mechanism of Cl secretion by canine tracheal epithelium. In control tissues with a mean calculated short-circuit current (Isc) of 18.1 microA/cm2, the intracellular Cl activity (aiCl) was 47.2 mM. This value is 30.1 mM (or 27.0 mV) above the electrochemical equilibrium for Cl across the apical membrane. Epinephrine, which stimulates Cl secretion, increased the calculated Isc to 160 microA/cm2 and decreased aiCl to 32.2 mM, a value only 11.2 mM (or 10.9 mV) above equilibrium for the apical membrane. These results indicate a secretagogue induced decrease in the impedance to Cl exist from the cell via the apical membrane. From these and prior measurements we calculate that epinephrine-induced Cl efflux from the cell can occur by simple diffusion across the apical membrane. Further implications of these calculations are also discussed.