Contribution of epoxyeicosatrienoic acids to the hypoxia-induced activation of Ca2+ -activated K+ channel current in cultured rat hippocampal astrocytes. Neuroscience 2006 Dec;143(3):703-16
Date
10/10/2006Pubmed ID
17027168DOI
10.1016/j.neuroscience.2006.08.021Scopus ID
2-s2.0-33750978403 (requires institutional sign-in at Scopus site) 45 CitationsAbstract
Brief hypoxia differentially regulates the activities of Ca(2+)-activated K(+) channels (K(Ca)) in a variety of cell types. We investigated the effects of hypoxia (<2% O(2)) on K(Ca) channel currents and on the activities of cytochrome P450 2C11 epoxygenase (CYP epoxygenase) in cultured rat hippocampal astrocytes. Exposure of astrocytes to hypoxia enhanced macroscopic outward K(Ca) current, increased the open state probability (NPo) of 71 pS and 161 pS single-channel K(Ca) currents in cell-attached patches, but failed to increase the NPo of both the 71 pS and 161 pS K(Ca) channel currents recorded from excised inside-out patches. The hypoxia-induced enhancement of macroscopic K(Ca) current was attenuated by pretreatment with tetraethylammonium (TEA, 1 mM) or during recording using low-Ca(2+) external bath solution. Exposure of astrocytes to hypoxia was associated with generation of superoxide as detected by staining of cells with the intracellular superoxide detection probe hydroethidine (HE), attenuation of the hypoxia-induced activation of unitary K(Ca) channel currents by superoxide dismutation with tempol, and as quantitated by high-pressure liquid chromatography/fluorescence assay using HE as a probe. In cultured astrocytes in which endogenous CYP epoxygenase activity has been inhibited with either miconazole or N-methylsulfonyl-6-(2-propargyloxyphenyl) hexanamide (MSPPOH) hypoxia failed to increase the NPo of both the 71 pS and 161 pS K(Ca) currents and generation of superoxide. Hypoxia increased the level of P450 epoxygenase protein and production of epoxyeicosatrienoic acids (EETs) from cultured astrocytes, as determined by immunohistochemical staining and LC/MS analysis, respectively. Exogenous 11,12-EET increased the NPo of both the 71 pS and 161 pS K(Ca) single-channel currents only in cell-attached but not in excised inside-out patches of cultured astrocytes. These findings indicate that hypoxia enhances the activities of two types of unitary K(Ca) currents in astrocytes by a mechanism that appears to involve CYP epoxygenase-dependent generation of superoxide and increased production or release of EETs.
Author List
Yamaura K, Gebremedhin D, Zhang C, Narayanan J, Hoefert K, Jacobs ER, Koehler RC, Harder DRMESH terms used to index this publication - Major topics in bold
AnimalsAnimals, Newborn
Astrocytes
Blotting, Western
Calcium Channel Blockers
Cell Hypoxia
Cells, Cultured
Chromatography, High Pressure Liquid
Cycloparaffins
Drug Interactions
Electric Stimulation
Enzyme Inhibitors
Fluorescent Antibody Technique
Glial Fibrillary Acidic Protein
Hippocampus
Indoles
Membrane Potentials
Patch-Clamp Techniques
Potassium Channels, Calcium-Activated
Rats
Reactive Oxygen Species
Superoxides
