Activation of Ca2+-Dependent K+ Channel and Cl- Conductance in Canine Pancreatic Acinar Cells through a Cyclic AMP Pathway

Effects of adenosine 3',5'-cyclic monophosphate (cAMP) on Ca2+ -dependent K+ channel and Cl- conductance in the plasma membrane of isolated canine pancreatic acinar cells were studied by patchclamp methods. In whole-cell current recordings on isolated cells dialyzed with K+ -rich solution containing 0.5 mM EGTA, addition of 0.5 mM dibutyryl cAMP (dbcAMP), or 50 μM forskolin to the bath increased outward K+ and inward Cl- currents associated with depolarizing and hyperpolarizing voltage jumps, respectively. In intact cells (cell-attached configurations), addition of 0.5 mM dbcAMP or 50 μM forskolin to the bath increased the opening of single K+ channel. In Ca2+ -free external solution (bath and pipette) 50 μM forskolin or 0.5 mM dbcAMP application evoked an increase in the opening of single K+ channel in intact cells. Addition of 0.5 mM dbcAMP to the bath solution containing 10 mM EGTA without Ca2+ increased the currents of whole-cell dialyzed with K+ -rich solution containing 10 mM EGTA. When cell was dialyzed with 20 mM EGTA, dbcAMP, or forskolin application did not increase the whole-cell currents. In excised inside-out patches, addition of the catalytic subunit of cAMP-dependent protein kinase (16 U/ml) in the presence of 0.3 mM ATP to the cytoplasmic face of membrane activated the K+ channel, but 0.1 mM cAMP did not. These results suggest that cAMP-dependent phosphorylation can activate Ca2+ -dependent K+ channels without increase in intracellular free Ca2+ and cAMP-dependent mechanism can activate Ca2+ -dependent Cl- conductances without the increase in Ca2+ in canine pancreatic acinar cells.