Increased generation of superoxide partly mediates brief hypoxia‐induced activation of cerebral arterial KCa channel currents

The mechanism of brief hypoxia‐induced activation of cerebral arterial Ca 2+ ‐activated K + channel currents (K Ca ) is not completely known. We investigated the role of generation of superoxide in the brief hypoxia‐evoked activation of K Ca channel currents in rat cerebral arterial muscle cells. Exposure of cerebral arterial muscle cells to brief hypoxia caused generation of intracellular superoxide as evidenced by intense staining of arterial muscle cells with the fluorescent probe hydroethydine, and quantitation of superoxide production using a fluorescent HPLC assay method. The level of superoxide averaged 0.51 ± 0.20 μM/ mg protein after 10 min normoxic incubation and 1.9 ± 0.12 μM/mg protein following 10 min exposure of the cerebral arterial muscle cells to brief hypoxia (p < 0.05, n = 4). Prior inhibition of CYP 4A ω‐hydroxylase activity with the suicide substrate inhibitor 17‐ODYA (5 μM) reduced the hypoxia‐induced production of superoxide to 0.78 ± 0.14 μM/mg protein (n = 4, p < 0.05). Exposure of patch‐clamped cerebral arterial muscle cells to hypoxia induced activation of a 238 pS single‐channel K Ca that was attenuated pretreatment with the superoxide dismutase mimic tempol (1 mM). These findings suggest that brief hypoxia‐induced CYP 4A ω‐hydroxylase‐dependent production of superoxide plays a role in signaling the hypoxia‐induced activation of cerebral arterial K Ca channel currents.