TASK-1 current is inhibited in a phosphorylation-dependent manner in myocytes from dogs with peri-operative AF. Myocytes were isolated from canine atrial myocardium at the time of atriotomy and after induction or failed induction of peri-operative AF. The methanandamide-sensitive TASK-1 current was measured by patch clamp recordings, and the average current density was plotted for pre-operative control (A, filled circles; n = 52 cells from 21 dogs), for peri-operative AF (B, filled circles; n = 19 cells from seven dogs), and for failed AF (C, filled circles; n = 12 cells from four dogs). Note that the TASK-1 current is absent from cells isolated after induction of peri-operative AF; however, addition of PP2A to the patch pipette rescued the current in cells isolated from the peri-operative AF dogs (B, open circles; n = 16 cells from seven dogs). PP2A caused no change in the current densities measured in cells from pre-operative control tissue (A, open circles; n = 50 cells from 20 dogs) or from dogs with failed AF induction (C, open circles; n = 5 cells from two dogs). The PP2A-rescued TASK-1 current density was not different from the current measured in cells from pre-operative control tissue (p > 0.05). Data are mean values ± S.E.