Platelet-activating factor activates cardiac GK via arachidonic acid metabolites.
Platelet-activating factor (PAF), added to the bathing solution, stimulated the cardiac muscarinic K+ channel (KACh) in the cell-attached patch (no agonist in the pipette). The PAF-induced KACh channel activation was blocked by WEB2086, a PAF-receptor inhibitor, indicating that the PAF-receptor mediated the response. PAF-induced activation was prevented by nordihydroguaieretic acid, a lipoxygenase inhibitor, and AA-861, a 5-lipoxygenase inhibitor, but was not affected by indomethacin, a cyclo-oxygenase inhibitor. The PAF-induced KACh channel activity disappeared upon formation of inside-out patch. In this inside-out patch, intracellular GTP alone induced maximal channel reactivation, which was inhibited by GDP-beta S. These results suggest that 5-lipoxygenase metabolites of PAF-released arachidonic acid cause a persistent stimulation of GK but not the KACh channel itself, resulting in a receptor-independent activation of the KACh channel by GTP.
Nakajima
T
T
2nd Department of Internal Medicine, Faculty of Medicine, University of Tokyo, Japan.
Sugimoto
T
T
Kurachi
Y
Y
D000818:Animals; D001095:Arachidonic Acids / Q000378:metabolism*; D016227:Benzoquinones / Q000494:pharmacology; D002478:Cells, Cultured; D044950:Flavanones; D005419:Flavonoids / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000494:pharmacology; D006168:Guinea Pigs; D006321:Heart / Q000187:drug effects* / Q000502:physiology; D006325:Heart Atria; D007213:Indomethacin / Q000494:pharmacology; D016859:Lipoxygenase Inhibitors / Q000494:pharmacology; D009637:Masoprocol / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism*; D010972:Platelet Activating Factor / Q000494:pharmacology*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D001095:Arachidonic Acids; D016227:Benzoquinones; D044950:Flavanones; D005419:Flavonoids; D016859:Lipoxygenase Inhibitors; D010972:Platelet Activating Factor; D015221:Potassium Channels; D010566:Virulence Factors, Bordetella; D016244:Guanosine 5'-O-(3-Thiotriphosphate); C006680:baicalein; D009637:Masoprocol; C036837:2,3,5-trimethyl-6-(12-hydroxy-5,10-dodecadiynyl)-1,4-benzoquinone; D006160:Guanosine Triphosphate; D019204:GTP-Binding Proteins; D007213:Indomethacin