DIRECT ACTION OF GENISTEIN ON CFTR

Human cystic fibrosis transmembrane conductance regulator (CFTR) chlor ide channels were expressed in oocytes from Xenopus laevis after injec tion of CFTR cRNA and studied with the two-electrode voltage-clamp and the giant patch techniques. The tyrosine kinase inhibitor genistein a lone activated a small chloride current in whole oocytes expressing CF TR and substantially increased the chloride current obtained upon stim ulation with forskolin and isobutyl methylxanthine (IBMX). In giant ex cised patches, genistein was unable to open protein-kinase-A-phosphory lated CFTR channels in the absence of ATP, but increased the ATP-induc ed CFTR channel currents by a factor of 3.8 +/- 1.7. This genistein-me diated potentiation in excised patches is independent of protein phosp hatase activity, as it is readily reversible, even after complete inhi bition of protein kinase A activity. Involvement of protein tyrosine k inases also seems unlikely, because this effect of genistein is not an tagonized by high concentrations of the tyrosine phosphatase inhibitor ortho-vanadate, We, therefore, propose a direct interaction of genist ein with CFTR, probably at a nucleotide binding site, which leads to a higher open probability.