Regulation of Na and Cl transport in sheep distal airways

Abstract

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.