EETs relax airway smooth muscle via an EpDHF effect: BK(Ca) channel activation and hyperpolarization.
Epoxyeicosatrienoic acids (EETs) are produced from arachidonic acid via the cytochrome P-450 epoxygenase pathway. EETs are able to modulate smooth muscle tone by increasing K(+) conductance, hence generating hyperpolarization of the tissues. However, the molecular mechanisms by which EETs induce smooth muscle relaxation are not fully understood. In the present study, the effects of EETs on airway smooth muscle (ASM) were investigated using three electrophysiological techniques. 8,9-EET and 14,15-EET induced concentration-dependent relaxations of the ASM precontracted with a muscarinc agonist (carbamylcholine chloride), and these relaxations were partly inhibited by 10 nM iberiotoxin (IbTX), a specific large-conductance Ca(2+)-activated K(+) (BK(Ca)) channel blocker. Moreover, 3 microM 8,9- or 14,15-EET induced hyperpolarizations of -12 +/- 3.5 and -16 +/- 3 mV, with EC(50) values of 0.13 and 0.14 microM, respectively, which were either reversed or blocked on addition of 10 nM IbTX. These results indicate that BK(Ca) channels are involved in hyperpolarization and participate in the relaxation of ASM. In addition, complementary experiments demonstrated that 8,9- and 14,15-EET activate reconstituted BK(Ca) channels at low free Ca(2+) concentrations without affecting their unitary conductance. These increases in channel activity were IbTX sensitive and correlated well with the IbTX-sensitive hyperpolarization and relaxation of ASM. Together these results support the view that, in ASM, the EETs act through an epithelium-derived hyperpolarizing factorlike effect.
Benoit
C
C
Le Bilarium, Faculty of Medicine, Department of Physiology and Biophysics, University of Sherbrooke, Sherbrooke, Quebec, Canada J1H 5N4.
Renaudon
B
B
Salvail
D
D
Rousseau
E
E
D015126:8,11,14-Eicosatrienoic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology*; D000818:Animals; D001685:Biological Factors / Q000378:metabolism*; D016084:Bronchoconstriction / Q000187:drug effects / Q000502:physiology; D002417:Cattle; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D051036:Large-Conductance Calcium-Activated Potassium Channels; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D018721:Muscarinic Agonists / Q000494:pharmacology; D009130:Muscle, Smooth / Q000187:drug effects* / Q000378:metabolism*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D010455:Peptides / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism*; D024681:Potassium Channels, Calcium-Activated; D011817:Rabbits; D014132:Trachea
D001685:Biological Factors; D016861:Cyclooxygenase Inhibitors; D004791:Enzyme Inhibitors; D051036:Large-Conductance Calcium-Activated Potassium Channels; D018721:Muscarinic Agonists; D010455:Peptides; D015221:Potassium Channels; D024681:Potassium Channels, Calcium-Activated; C067410:endothelium-dependent hyperpolarization factor; C046783:11,12-epoxy-5,8,14-eicosatrienoic acid; C064719:iberiotoxin; C040776:5,6-epoxy-8,11,14-eicosatrienoic acid; C050715:8,9-epoxyeicosatrienoic acid; C046782:14,15-epoxy-5,8,11-eicosatrienoic acid; D019001:Nitric Oxide Synthase; D015126:8,11,14-Eicosatrienoic Acid