TI - Functional characterization of CFTR in MAEC . AB - Subsequently , we have investigated the functional expression of CFTR in wild type MAEC . Application of the PHOSphorylating cocktail , containing10 muM forskolin and 100 muM IBMX , activated in these cells a current without any apparent rectification and voltage -independent kinetics , which reversed at -26 + - 6 mV ( n = 6 ) , i.e.close to the Cl-equilibrium potential , ECl ( figure 2A ) . Its phenotype was completely different from that of Cl - currents activated by loading the cells with Ca2+ ( figure 2B ) , which are outwardly rectifying , slowly activate at positive potentials and inactivate at potentials negative to ECl [13 , 14] . Challenging the MAEC with a 25 % hypotonic extracellular solution activated another type of Cl - current that inactivates at positive potentials and shows a less pronounced outward rectification ( figure 2C ) . The latter currents have been described in detail in other EC as VRAC , volume-regulated anion currents [6 , 15 , 16] . The cAMP -activated current reached a stationary value approximately 2 minutes after application of the phosphorylaTING cocktail ( figure 3A ) , and disappeared after wash-out of the PHOSphorylation cocktail . The cAMP -activated current was observed in 16 out of 22 cells , but its density was rather small ( 49 + - 11 pA/pF at +50 mV , obtained from voltage ramps , n = 16 ) compared to that of the other Cl - currents . It was activated without any change in cell volume or elevation of intracellular Ca2+ . Glibenclamide ( 50 muM ) blocked the c-AMP -activated current by 62 + - 4 % ( n = 6 ) ( figure 3D ) . Obviously , the profile of this current is similar to that of CFTR currents in other tissues , i.e.slow activation , linear I-V curve , time -independent kinetics and inhibition by glibenclamide , indicating that CFTR channels are also functionally expressed in MAEC , and coexist with atleast two other types of Cl-channels .