Background. Voltage-gated potassium channels (Kv) channels have been proposed to be one of the downstream effectors activated by hypoxia in pulmonary arterial smooth muscle cells (PASMCs) [1, 2]. Different Kv channel types contribute to the delayed rectified potassium current in PASMCs, with their relative level of expression in PASMCs related to the caliber of artery. The expression of Kv1.5 alpha subunit increases in a manner inversely related to pulmonary arterial diameter and is highest in PASMCs from the near resistance-sized arteries that exhibit the greatest constriction in response to hypoxia [3]. Previous studies of our group have suggested that AMPK activation mediates the hypoxic pulmonary vasoconstriction [4]. The aim of this work was, therefore, to investigate whether AMPK regulates in a similar manner Kv1.5 stably expressed in HEK 293 cells and the native Kv current of PASMCs from pulmonary arteries with an internal diameter less than 200 microns.Methods. PASMCs were isolated as described previously [4]. Kv currents were recorded from these and from HEK293 cell that stably expressed Kv1.5, using whole-cell patch clamp in voltage-clamp mode, and with a holding potential of -80 mV (PASMCs) or -60 mV (HEK 293). Kv currents were assessed by ramp protocol (e.g., -100 to +40mV) followed by a single voltage step to either +40 mV (PASMCs) or +50 mV (HEK 293). Data are expressed as I/Izero (means ± S.E.M, n=3-7), where Izero is the current magnitude recorded at the onset of the experimental interventions.Results. AMPK activation markedly attenuated the macroscopic currents throughout the current-voltage ramp in both PASMCs and in HEK 293 cells that stably expressed Kv1.5. Application of the AMPK activator 100μM A-769662 led to inhibition of outward K+ currents by -26.5 ± 5 % and -35.8± 7 %, in PASMC and Kv1.5, respectively. Moreover, intracellular dialysis of an active AMPK heterotrimer (α2β2γ1, thiophosphorilated) also inhibited Kv currents by -28 ± 6 % and -28.6 ± 2 %, in PASMCs and Kv1.5 respectively. By contrast, current inhibition was not observed upon intracellular dialysis of an inactive AMPK heterotrimer (α2D157A). The AMPK inhibitor compound C (40μM) blocked inhibition of Kv1.5 by A769662 in HEK 293 cells. However, confounding inhibition of Kv by compound C in PASMCs precluded accurate assessment of the effects of this agent on A769662 action in PASMCs. Conclusion. Consistent with the proposal that AMPK mediates the effects of hypoxia on pulmonary arterial myocytes, AMPK inhibits Kv1.5 currents in HEK293 cells and the delayed rectifier in PASMCs acutely isolated from resistance size pulmonary arteries.