CYTOSOLIC [CL-] REGULATES NA- ROLES OF CAMP AND CL- CHANNELS( ABSORPTION IN FETAL ALVEOLAR EPITHELIUM )

We studied the regulatory mechanism of Na+ absorption in fetal distal lung epithelium (FDLE), using patch clamp and single cell imaging tech niques. A beta(2)-agonist activated a 28 pS non-selective cation chann el (NSCC) by: 1) producing a dependency of the NSCC activity on the cy tosolic [Cl-] ([Cl-](c)); 2) inducing a reduction in the [Cl-](c) from 45 to 25 mM which directly activated the beta(2)-treated NSCC. The be ta(2)-agonist-induced decrease in [Cl-](c) was caused by activation of Ca2+-activated K+ channel and cAMP-activated Cl- channel. A developme nt of the [Cl-](c)-dependency and a reduction in [Cl-](c) act as a sec ond messenger of the beta(2) agonist signal transduction pathway in th is Na+ transporting epithelium.