Effect of HCO3 − on TPA- and IBMX-induced anion conductances in Necturus gallbladder epithelial cells

Abstract

Effects of HCO3 − on protein kinase C (PKC)- and protein kinase A (PKA)-induced anion conductances were investigated in Necturus gallbladder epithelial cells. In HCO3 −-free media, activation of PKC via 12- O-tetradecanoylphorbol 13-acetate (TPA) depolarized apical membrane potential ( V a) and decreased fractional apical voltage ratio (FR). These effects were blocked by mucosal 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB), a Cl− channel blocker. In HCO3 −media, TPA induced significantly greater changes in V a and FR. These effects were blocked only when NPPB was present in both mucosal and basolateral compartments. The data suggest that TPA activates NPPB-sensitive apical Cl− conductance ( g Cl a) in the absence of HCO3 −; in its presence, TPA stimulated both NPPB-sensitive g Cl a and basolateral Cl− conductance ( g Cl b). Activation of PKA via 3-isobutyl-1-methylxanthine (IBMX) also decreased V a and FR; however, these changes were not affected by external HCO3 −. We conclude that HCO3 − modulates the effects of PKC on g Cl b. In HCO3 − medium, TPA and IBMX also induced an initial transient hyperpolarization and increase in intracellular pH. Because these changes were independent of mucosal Na+ and Cl−, it is suggested that TPA and IBMX induce a transient increase in apical HCO3 −conductance.