Mechanisms for the inhibition of amiloride-sensitive Na⁺ absorption by extracellular nucleotides in mouse trachea

Abstract.

Purinergic stimulation of airway epithelial cells induces Cl^– secretion and modulates Na⁺ absorption by an unknown mechanism. To gain insight into this mechanism, we used a perfused micro-Ussing chamber to assess transepithelial voltage (V _te) and amiloride-sensitive short-circuit current (I _sc-Amil) in mouse trachea. Exposure to apical ATP or UTP (each 100 µmol/l) caused a large initial increase in lumen negative V _te and I _sc, corresponding to a transient Cl^– secretion, while basolateral application of ATP/UTP induced only a small secretory response. Luminal, but not basolateral, application of nucleotides was followed by a sustained and reversible inhibition of I _sc-Amil that was independent of extracellular Ca²⁺ or activation of protein kinase C and was not induced by carbachol (100 µmol/l) or the Ca²⁺ ionophore ionomycin (1 µmol/l). Removal of extracellular Cl^– or exposure to 200 µM DIDS reduced UTP-mediated inhibition of I _sc-Amil substantially. The phospholipase inhibitor U73122 (10 µmol/l) and pertussis toxin (PTX; 200 ng/ml) both attenuated UTP-induced Cl^– secretion and inhibition of I _sc-Amil. Taken together, these data imply a contribution of Cl^– conductance and PTX-sensitive G proteins to nucleotide-dependent inhibition of the amiloride-sensitive Na⁺ current in the mouse trachea.