Action of tetraethylammonium on calcium-activated potassium channels in pig pancreatic acinar cells studied by patch-clamp single-channel and whole-cell current recording.

The effects of tetraethylammonium ions on currents through high-conductance voltage- and Ca2+-activated K+ channels have been studied with the help of patch-clamp single-channel and whole-cell current recording on pig pancreatic acinar cells. In excised outside-out membrane patches TEA (1 to 2 mM) added to the bath solution virtually abolishes unitary current activity except at very positive membrane potentials when unitary currents corresponding to a markedly reduced conductance are observed. TEA in a lower concentration (0.2 mM) markedly reduces the open-state probability and causes some reduction of the single-channel conductance. In inside-out membrane patches bath application of TEA in concentrations up to 2 mM has no effect on single-channel currents. At a higher concentration (10 mM) slight reductions in single-channel conductance occur. In whole-cell current recording experiments TEA (1 to 2 mM) added to the bath solution completely suppresses the outward currents associated with depolarizing voltage jumps to membrane potentials of 0 mV and blocks the major part (70 to 90%) of the outward currents even at very positive membrane potentials (30 to 40 mV). In contrast TEA (2 mM) added to the cell interior (pipette solution) has no effect on the outward K+ current. Our results demonstrate that TEA in low concentrations (1 to 2 mM) acts specifically on the outside of the plasma membrane to block current through the high-conductance Ca2+- and voltage-activated K+ channels.