Regulation of Na and Cl transport in sheep distal airways.

To investigate ion transport function of distal airways mucosa we dissected and isolated segments of sheep bronchioles (outside diameter 664 +/- 10 microns, means +/- SE). Both ends of a segment were cannulated with glass micropipettes, and the preparation was placed in a bath and perfused with oxygenated Krebs-Henseleit solution at 37 degrees C. Luminal amiloride (0.1 mM) reduced potential difference (PD) from 3.06 +/- 0.68 mV to 1.08 +/- 0.24 mV (n = 5, P < 0.02). Submucosal ouabain (0.1 mM) decreased PD from 1.82 +/- 0.38 to 0.07 +/- 0.02 mV (n = 5, P < 0.009). Submucosal bumetanide (0.1 mM) caused a decline in PD from 3.44 +/- 0.98 to 2.75 +/- 0.71 mV (n = 19, P < 0.03). Exposure of the lumen to Cl channel blocker diphenylamine-2-carboxylate (1 mM) depolarized the bronchiole from a PD of 4.46 +/- 1.7 mV to 2.50 +/- 0.97 mV (n = 7, P < 0.03). Submucosal adenosine 3',5'-cyclic monophosphate (cAMP) analogue, 8-(4-chlorophenylthio)-cAMP (0.1 mM), raised PD from 3.45 +/- 1.08 to 3.82 +/- 1.24 mV (n = 10, P < 0.05). In eight experiments submucosal 0.1 mM carbachol, which elevates cytosolic Ca, resulted in rapid hyperpolarization (P < 0.02) followed by amiloride-inhibitable slow depolarization (P < 0.05). The data provide evidence for the presence in the sheep bronchiolar epithelium of active Na absorption that depends on a basolaterally located Na-K-ATPase ion pump. Increased cytosolic Ca probably inhibits Na absorption. The epithelium also has a Cl secretory process through apical Cl channels.