Involvement of CFTR in oviductal HCO3- secretion and its effect on soluble adenylate cyclase-dependent early embryo development

BACKGROUND: The cystic fibrosis transmembrane conductance regulator (CFTR) plays a critical role in electrolyte and fluid transport in epithelial cells, and women with cystic fibrosis (CF), caused by CFTR gene mutations, have a higher incidence of infertility. METHODS: In the present study, we investigated the expression of CFTR in porcine oviduct and its functional role in oviductal HCO3- secretion and embryo development with RT-PCR, western blot, patch-clamp, short-circuit current (I-sc), pH measurement and embryo culture. RESULTS: RT-PCR and western blot analysis showed the expression of CFTR mRNA and protein in the oviduct with its localization demonstrated by immunohistochemstry. The whole-cell patch-clamp recording revealed a forskolin (FSK)-activated current with electrophysiological and pharmacological characteristics of CFTR. The I measurement showed that FSK-stimulated an increase in the I-sc, which could be significantly reduced by CFTR inhibitor or removal of both CO2 and HCO3-. pH measurement showed a FSK stimulated alkalization at the apical surface, which could be inhibited by CFTR inhibitor, indicating CFTR-mediated HCO3- secretion. Mouse embryo development from 2-cell to morula or blastocyst stage was significantly inhibited in the absence of HCO3- or when co-cultured with HCO3- secretion-deficient CFTR mutant cells as compared with the wild-type. RT-PCR, western blot and immunostaining showed the expression of soluble adenylate cyclase (sAC), the known HCO3- sensor, in embryos. Treatment with its inhibitors, 2-hydroxyestradiol and KH7, prevented the HCO3- dependent embryo development. CONCLUSION: The present results suggest that CFTR-mediated oviductal HCO3- secretion may be vital for sAC-dependent early embryo development, a defect of which may contribute to the reduced fertility seen in women with CF.