Interdependence of Na+ and Cl- transport in dog tracheal epithelium.

Previous studies showed active transport of Cl- toward and of Na+ away from the luminal surface of dog tracheal epithelium. The possible interdependence of Cl- and Na+ fluxes has not been explored fully in this preparation. The purpose of the present study is to investigate the relationship between these fluxes. Substituting choline for Na+ in the media bathing dogs tracheal epithelium reduced net Cl- transport toward the lumen from 1.86 +/- SE 0.27 to 0.49 +/- SE 0.20 mueq.cm-2.h-1. Substituting SO4(2-) For Cl- decreased net Na+ flux toward the lumen from -1.05 +/- SE 0.20 to -1.78 +/- SE 0.36 mueq.cm-2.h-1. Acetylcholine (5 x 10(-4) M) and terbutaline (10(-5) M) increased and furosemide (10(-3) M) decreased net Cl- transport toward the lumen in control, but not in Na+ free bathing media. Acetylcholine increased net Na+ flux toward the lumen in control, but not in Cl- free bathing media. Thus this study showed that 1) in media lacking Na+, net Cl- flux toward the lumen is decreased, and vice versa, 2) the increases in Cl- transport toward the lumen due to acetylcholine and terbutaline and the decrease due to furosemide required Na+ and 3) in the increase in Na+ flux toward the lumen due to acetylcholine required Cl-. These findings indicate that there is an interdependence of Cl- and Na+ fluxes in dog tracheal epithelium.