Ion transport by sheep distal airways in a miniature chamber

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<degrees>C and oxygenated. Pooled data from 27 distal airways showed an inner airway diameter of 854 +/- 22 (SE) mum and a transepithelial potential difference (PD) of 1.86 +/-0.29 mV, lumen negative. Short-circuit current (I-sc) was 25 +/-3.5 muA/cm(2), tissue resistance was 96 +/- 14 Omega, and conductance was 15.2 +/-1.7 mS/cm(2). At baseline, amiloride-sensitive Na transport accounted for 51% of I-sc (change in I-sc = 9.7 +/-2.6 muA/cm(2); n = 8 airways), corresponding to 0.36 mu eq.cm(-2).h(-1). Treatment with 0.1 mM bumetanide did not reduce the I-sc (n = 5 airways). Exposure to 1 muM Ca ionophore A-23187 raised the I-sc by 9 muA/cm(2) (47%; P < 0.03; n = 6 airways). The latter effect was blunted by bumetanide. Carbachol at 1 <mu>M provoked a biphasic response, an initial rapid rise in I-sc followed 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.