cAMP- but not Ca2+-regulated Cl- conductance in the oviduct is defective in mouse model of cystic fibrosis

Defective adenosine 3',5'-cyclic monophosphate (cAMP)-mediated Cl- transport in cystic fibrosis (CF) reflects defects in the cystic fibrosis transmembrane conductance regulator (CFTR). A moderate level of CFTR mRNA expression has been found in rodent and human oviductal epithelium, but unlike other CFTR-expressing tissues, the oviduct in CF patients is apparently normal. The present study was carried out to investigate the relative magnitude of the cAMP- and intracellular Ca2+ (Ca(i)/2+)- regulated Cl- secretion in primary cultures of the oviduct from normal and CF mice generated by targeted disruption of the murine CF gene. Normal oviductal epithelium exhibited a basal equivalent short-circuit current (I(eq)) of 20.3 ± 1.7 μA/cm2. CF oviduct exhibited a lower basal I(eq) of 4.5 ± 1.9 μA/cm2. In normal mice, forskolin (10-5 M, apical) elicited a slowly developing sustained rise in I(eq), whereas ionomycin (5 x 10-6 M, apical) and ATP (10-4 M, apical) induced larger increases in I(eq) consisting of a prompt, transient response followed by a slowly decreasing component. The I(eq) response to forskolin was totally abolished in CF mouse oviducts, but the magnitudes of the peak I(eq) responses to ionomycin and ATP were not different from normal. The time courses of the ionomycin- and ATP- evoked responses, however, were significantly more transient in CF than in normal oviducts. These results demonstrate that CF mouse oviduct exhibits defective cAMP- but not Ca(i)/2+-mediated Cl- secretion. The relatively high level of functional expression of the alternative Ca2+-activated Cl- secretory pathway in the mouse oviduct may contribute to the absence of major pathology in the CF oviduct.