Ion transport and metabolic effects of amiloride in canine tracheal mucosa

We studied the interaction between Cl transport and the Na entry step at the luminal side of the canine tracheal epithelium by testing the effects of amiloride, an inhibitor of apical membrane Na conductance. The tracheal mucosa was mounted as a flat sheet in Ussing chamber and bathed with Krebs-Henseleit solution. In six experiments²²Na and³⁶Cl transepithelial fluxes were determined. Under basal conditions net Na absorption was 0.45±0.10 µEq/cm²·h ( \(\bar X\) ±SE) and declined to 0.07±0.08 after 0.1 mM amiloride was added to the mucosal bath. No changes were found in Cl fluxes. Addition of amiloride (0.1 mM) to the luminal bath usually caused a 10–20% decline in short circuit current (SCC). However, these alterations in SCC were often transient when the bathing media contained Cl. In contrast, in the absence of Cl the inhibition of SCC by 0.01 mM mucosal amiloride was predictable, large, and stable (ΔSCC=?21±6 µA/cm²,N=5). Addition of higher concentration of amiloride (2–4 mM) to the submucosal side (N=6) caused significant decline in net Cl secretion from 1.67±0.37 to 0.06±0.25 µEq/cm² · h (P<0.02). These changes were probably caused by inhibition of tissue metabolism since 2 mM amiloride caused a 73% fall in tissue oxygen consumption. Ouabain (0.1 mM), which inhibits Na-K-ATPase and therefore both Na and Cl transport, reduced tissue O₂ consumption by 34%. The Na entry step at the luminal membrane is amiloride sensitive, but does not appear to be crucial for the maintenance of the Cl secretory process. Luminal membrane conductance appears to be primarily a Cl-conductance. About one third of tissue O₂ demands are utilized for transport of Na and Cl.