Ethanol exposure affects CFTR-mediated chloride secretion through modulation of cellular cAMP level Upon adenosine binding, the A 2B AR signals through G s protein to activate adenylyl cyclase and raises intracellular cAMP [13, 32] . Because CFTR is a cAMP-activated chloride channel, we hypothesized that ethanol inhibits adenosine-stimulated cAMP production to cause a reduced CFTR channel activity. To test this hypothesis, air-liquid interface cultures of Calu-3 cells were exposed basolaterally to either 0 mM or 100 mM of ethanol for 24 hours. These cells were apically stimulated with 100 mM of adenosine as described above for 10 minutes, the time point at which the epithelial I SC was at its peak levels. Then, the cells were lysed and the levels of cellular cAMP assayed. The results demonstrate that ethanol pre-treatment significantly decreased adenosine-stimulated cAMP levels (p,0.05, n = 5) (Fig. 5A ). In addition, to test whether the decrease in cAMP was in fact causing the suppression of adenosine-stimulated chloride transport by ethanol, Sp-cAMPS, a cell permeable and phosphodiesteraseresistant cAMP analogue, was used to directly activate PKA which then activates the CFTR channel. As shown in Figure 5B , the alcohol-treated Calu-3 cells in the presence of 10 mM Sp-cAMPS obliterated the ethanol suppressive effect on adenosine-induced chloride secretion (p,0.05, n = 6). Thus, we conclude that ethanol inhibits CFTR-mediated chloride secretion by directly affecting the cellular cAMP level instead of the downstream PKA enzyme.