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) (GTP-gamma-S) (in the presence and absence of ACh in the pipette, respectively). Slope conductance, the response to GTP and GTP-gamma-S, 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.