Acetylcholine-sensitive potassium channels in human atrial myocytes

Single channel recording techniques were used to study acetylcholine (ACh)-sensitive K⁺ channel activity in human atrial myocytes isolated from specimens obtained during corrective cardiac surgery. Under conditions of cell-attached patch, the presence of ACh in the patch pipette activated K⁺ channels. Single channel activity occurred in periodic bursts. The channels exhibited a slope conductance of 46 ± 2 pS inwardly (means ± SD, n = 4). During a burst, both open and closed time histograms were fitted by a single exponential curve,suggesting the existence of one open and one closed state during a burst. Open probability increased directly with ACh concentration without affecting open time. The channel could be activated by GTP and guanosine 5'-O- (3-thiotriphosphate) (GTPγS) (in the presence and absence of ACh in the pipette, respectively). Slope conductance, the response to GTP and GTPγS, and the independence of activation from Ca²⁺ were similar to those for other species. In contrast, sensitivity to ACh appeared diminished compared with frog atrial myocytes.