Addition of cAMP to mucosal or serosal medium induces different actions on Necturus gallbladder

Open tip and Cl(-)-selective microelectrodes were used to study the effects of cAMP on apical membrane potential (Va), fractional voltage ratio (fa) and intracellular chloride activity (aicl) in Necturus gallbladder under open-circuit conditions. In the presence of cAMP in the mucosal medium Va depolarized from -68 +/- 5 mV in control conditions to -56 +/- 5 mV and fa decreased from 0.56 +/- 0.15 in control conditions to 0.15 +/- 0.02. Concomitantly aicl fell from 15 +/- 2 mM to 8 +/- 3 mM, a value close to its electrochemical equilibrium activity. These results differ markedly from those obtained when cAMP was added to serosal medium and indicate that cAMP elicits different transport mechanisms whether it is added to the serosal medium or to the mucosal medium.