[en] The acid-sensitive, two-pore domain K(+) channel, TASK-1, contributes to the background K(+) conductance and membrane potential (Em) of rat and human pulmonary artery (PA) smooth muscle cells (SMC), but its role in regulating tone remains elusive. This study aimed to clarify the role of TASK-1 by determining the functional properties of PA from mice in which the TASK-1 gene was deleted (TASK-1/3 KO), in comparison with wild type (WT) C57BL/6 controls. Small vessel wire myography was used to measure isometric tension developed by intact PA. Em and currents were recorded from freshly isolated PASMC using the perforated patch-clamp technique. Reverse-transcription polymerase chain reaction (RT-PCR) was used to estimate K(+) channel expression. We could find no difference between PA from WT and TASK-1/3 KO TASK KO mice. They showed similar constrictor responses to a range of agonists and K(+) concentrations, the K(+) channel blockers 4-aminopyridine, tetraethylammonuim ions and XE991. Treprostinil, proposed to dilate by activating TASK-1, was just as effective in TASK-1/3 KO arteries. Blocking Ca(2+) influx with nifedipine (1 muM) or levcromakalim (10 muM) had no effect on resting tone in either strain. The resting Em of PASMC and its responses to K(+) channel blockers were unchanged in TASK-1/3 KO mice as were voltage-activated K(+) currents, including the non-inactivating K(+) current (I(KN)) measured at 0 mV. The Em was, however, depolarised in comparison with other species. Mouse I(KN) was much smaller than in rat and showed no sensitivity to pH. The results imply that TASK-1 does not form a functional channel in mouse PASMC.