Differential activation of the HCO3‐ conductance through the cystic fibrosis transmembrane conductance regulator anion channel by genistein and forskolin in murine duodenum

Abstract

Many cystic fibrosis (CF)-associated mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) anion channels affect CFTR-activated HCO(3)(-) transport more than Cl(-) transport. Targeting the CFTR HCO(3)(-) conductance, if possible, may therefore be of major therapeutic benefit. In the present study, we examined the effects of genistein and forskolin on duodenal mucosal HCO(3)(-) and Cl(-) secretion. Murine duodenal mucosal HCO(3)(-) and Cl(-) secretions were examined in vitro in Ussing chambers by the pH stat and short circuit current (I(sc)) techniques. Genistein markedly stimulated duodenal HCO(3)(-) secretion and I(sc) in a dose-dependent manner in CFTR wild-type mice, but not in CFTR null mice. CFTR(inh)-172, a highly specific CFTR inhibitor, inhibited genistein-stimulated duodenal HCO(3)(-) secretion and I(sc) in wild-type mice. Genistein induced 59% net HCO(3)(-) increase and 123% net I(sc) increase over basal value, whereas forskolin, an activator of adenylate cyclase, induced 94% net HCO(3)(-) increase and 507% net I(sc) increase, indicating that, compared with forskolin, genistein induced a relatively high HCO(3)(-)/I(sc) ratio. Further data showed that CFTR HCO(3)(-)/Cl(-) conductance ratio was 1.05 after genistein stimulation, whereas after forskolin stimulation, the CFTR HCO(3)(-)/Cl(-) conductance ratio was 0.27. Genistein stimulates duodenal HCO(3)(-) and Cl(-) secretion through CFTR, and has a relatively high selectivity for the CFTR HCO(3)(-) conductance, compared with forskolin. This may indicate the feasibility of selective targeting of the HCO(3)(-) conductance of the CFTR channels.