Ion transport by sheep distal airways in a miniature chamber

Abstract

Ion transport and the electric profile of distal airways of sheep lungs were studied in a miniature polypropylene chamber with a 1-mm aperture. Small airways with an inner diameter < 1 mm were isolated, opened longitudinally, and then mounted as a flat sheet onto the 1-mm aperture where it was glued and secured with an O-ring. Both sides of the tissue were bathed with identical physiological solutions at 37°C and oxygenated. Pooled data from 27 distal airways showed an inner airway diameter of 854 ± 22 (SE) μm and a transepithelial potential difference (PD) of 1.86 ± 0.29 mV, lumen negative. Short-circuit current ( I sc) was 25 ± 3.5 μA/cm2, tissue resistance was 96 ± 14 Ω, and conductance was 15.2 ± 1.7 mS/cm2. At baseline, amiloride-sensitive Na transport accounted for 51% of I sc (change in I sc = 9.7 ± 2.6 μA/cm2; n = 8 airways), corresponding to 0.36 μeq · cm−2 · h−1. Treatment with 0.1 mM bumetanide did not reduce the I sc( n = 5 airways). Exposure to 1 μM Ca ionophore A-23187 raised the I sc by 9 μA/cm2(47%; P < 0.03; n = 6 airways). The latter effect was blunted by bumetanide. Carbachol at 1 μM provoked a biphasic response, an initial rapid rise in I scfollowed by a decline ( n = 3 airways). There was no significant increase in PD or I sc in response to isoproterenol or dibutyryl cAMP. The data suggest that Na absorption constitutes at least 50% of baseline transport activity. Cl or other anion secretion such as HCO3 appears to be present and could be stimulated by raising intracellular Ca.