In the systemic circulation,
11,12-epoxyeicosatrienoic acid (11,12-EET) elicits
nitric oxide (NO)- and
prostacyclin-independent vascular relaxation, partially through the activation of large conductance Ca(2+)-activated
potassium (
BK) channels. However, in the lung
11,12-EET contributes to
hypoxia-induced pulmonary vasoconstriction. Since pulmonary artery smooth muscle cells also express
BK channels, we assessed the consequences of BKβ(1) subunit deletion on pulmonary responsiveness to
11,12-EET as well as to acute
hypoxia. In
buffer-perfused mouse lungs,
hypoxia increased pulmonary artery pressure and this was significantly enhanced in the presence of
NO synthase (NOS) and
cyclooxygenase (COX) inhibitors. Under these conditions the elevation of tissue EET levels using an inhibitor of the soluble
epoxide hydrolase (sEH-I), further increased the hypoxic contraction. Direct administration of
11,12-EET also increased pulmonary artery pressure, and both the sEH-I and
11,12-EET effects were prevented by
iberiotoxin and absent in BKβ(1)(-/-) mice. In pulmonary artery smooth muscle cells treated with NOS and COX inhibitors and loaded with the potentiometric
dye,
di-8-ANEPPS,
11,12-EET induced depolarization while the
BK channel opener
NS1619 elicited hyperpolarization indicating there was no effect of the EET on classical plasma membrane
BK channels. In pulmonary artery smooth muscle cells a subpopulation of
BK channels is localized in mitochondria. In these cells,
11,12-EET elicited an
iberiotoxin-sensitive loss of mitochondrial membrane potential (JC-1 fluorescence) leading to plasma membrane depolarization, an effect not observed in BKβ(1)(-/-) cells. Mechanistically, stimulation with
11,12-EET time-dependently induced the association of the BK α and β(1) subunits. Our data indicate that in the absence of NO and
prostacyclin 11,12-EET contributes to pulmonary vasoconstriction by stimulating the association of the α and β(1) subunits of mitochondrial
BK channels. The 11,12-EET-induced activation of
BK channels results in loss of the mitochondrial membrane potential and depolarization of the pulmonary artery smooth muscle cells.