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-channel activity by
5,6- and 11,12-EET
Le Bilarium, Department of Physiology and Biophysics, Faculty of Medicine, University of Sherbrooke, Sherbrooke, Quebec, Canada J1H 5N4
Using microelectrode potential measurements, we
tested the involvement of
Cl
conductances in the
hyperpolarization induced by 5,6- and 11,12-epoxyeicosatrienoic acid
(EET) in airway smooth muscle (ASM) cells. 5,6-EET and 11,12-EET (0.75 µM) caused 
5.4 ± 1.1- and 3.34 ± 0.95-mV hyperpolarizations, respectively, of rabbit tracheal cells
(from a resting membrane potential of 53.25 ± 0.44 mV), with significant residual repolarizations remaining after the
Ca2+-activated
K+ channels had been blocked by 10 nM iberiotoxin. In bilayer reconstitution experiments, we demonstrated
that the EETs directly inhibit a Ca2+-insensitive
Cl channel from bovine ASM;
1 µM 5,6-EET and 1.5 µM 11,12-EET lowered the unitary current
amplitude by 40 (n = 6 experiments)
and 44.7% (n = 4 experiments),
respectively. Concentration-dependent decreases in channel open
probability were observed, with estimated
IC50 values of 0.26 µM for 5,6- and 1.15 µM for 11,12-EET. Furthermore, pharmacomechanical tension
measurements showed that both regioisomers induced significant
bronchorelaxations in epithelium-denuded ASM strips. These results
suggest that 5,6- and 11,12-EET can act in ASM as epithelium-derived
hyperpolarizing factors.
membrane potential; airway smooth muscle; epithelium-derived hyperpolarizing factor; epoxyeicosatrienoic acid; chloride channel; eicosanoids; tension measurements; bronchorelaxation
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