Fig. 9.

ATP increases transepithelial Cl⁻ secretion in polarized biliary monolayers. Short-circuit current (I_sc) across normal rat cholangiocyte (NRC) monolayers was measured under voltage-clamp conditions in an Ussing chamber. In these representative recordings agonists are added to the apical chamber. A: simultaneous addition of cpt-cAMP (500 μM) and 3-isobutyl-1-methylxanthine (IBMX, 100 μM) increased I_sc, and subsequent addition of ATP (100 μM) resulted in a further significant increase in the magnitude of the I_sc (top tracing). In the presence of CFTR_inh-172 (5 μM) cpt-cAMP-IBMX failed to increase I_sc; however, the ATP-stimulated increase in I_sc was unaffected (bottom tracing). B: cumulative data showing the average change in I_sc after addition of cpt-cAMP-IBMX or ATP in the presence or absence of CFTR_inh-172. The y-axis values are reported as ΔI_sc (maximum I_sc − basal I_sc). *CFTR_inh-172 significantly inhibited the cpt-cAMP-IBMX-induced increase in I_sc (P < 0.01, n = 4 each) **Extracellular ATP added to the apical chamber significantly increased I_sc vs. cpt-cAMP-IBMX (P < 0.05, n = 4). C: in this representative recording, addition of ATP (100 μM) to the apical bath increases I_sc (top tracing). In the presence of U73122, the ATP-stimulated I_sc is inhibited. D: cumulative data demonstrating the average change in ATP-stimulated I_sc in the presence of suramin, U73122, or 2-APB. The y-axis values are reported as ΔI_sc (maximum I_sc − basal I_sc). *Suramin (n = 4, P < 0.05), U73122 (n = 7, P < 0.01), or 2-APB (n = 6, P < 0.05) each significantly inhibited the ATP-stimulated increase in I_sc.