Epoxyeicosatrienoic acids activate K+ channels in coronary smooth muscle through a guanine nucleotide binding protein.
Epoxyeicosatrienoic acids (EETs) are endothelium-derived arachidonic acid metabolites of cytochrome P450. They dilate coronary arteries, open K+ channels, and hyperpolarize vascular smooth muscles. However, the mechanisms of these smooth muscle actions remain unknown. This study examined the effects of EETs on the large-conductance Ca(2+)-activated K+ channel (KCa) in smooth muscle cells of small bovine coronary arteries. In cell-attached patch-clamp experiments, 11,12-EET produced a 0.5- to 10-fold increase in the activity of the KCa channels when added in concentrations of 1, 10, and 100 nmol/L. In the inside-out excised membrane patch mode, 11,12-EET was without effect on the activity of the KCa channel unless GTP (0.5 mmol/L) or GTP and ATP (1 mmol/L) were added to the bath solution. In the presence of GTP and ATP, the increase in the KCa channel activity with 11,12-EET in inside-out patches was comparable to that in cell-attached patches. This effect of 11,12-EET in inside-out patches was blocked by the addition of GDP-beta-S (100 mumol/L). In outside-out patches, 11,12-EET also increased the KCa channel activity when GTP and ATP were added to the pipette solution. The addition of a specific anti-Gs alpha antibody (100 nmol/L) in the pipette solution completely blocked the activation of the KCa channels induced by 11,12-EET. An anti-G beta gamma or anti-Gi alpha antibody was without effect. We conclude that 11,12-EET activates the KCa channels by a Gs alpha-mediated mechanism. This mechanism contributes to the effects of EETs as endothelium-derived hyperpolarizing factors to hyperpolarize and relax arterial smooth muscle.
Li
P L
PL
Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee 53226, USA.
Campbell
W B
WB
D015126:8,11,14-Eicosatrienoic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D000906:Antibodies / Q000276:immunology; D001158:Arteries / Q000502:physiology; D002118:Calcium / Q000502:physiology; D002352:Carrier Proteins / Q000378:metabolism*; D002417:Cattle; D002772:Cholera Toxin / Q000494:pharmacology; D003331:Coronary Vessels / Q000166:cytology / Q000378:metabolism*; D004553:Electric Conductivity; D019204:GTP-Binding Proteins / Q000276:immunology; D006150:Guanine Nucleotides / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects* / Q000502:physiology; D013873:Thionucleotides / Q000494:pharmacology
D000906:Antibodies; D002352:Carrier Proteins; D006150:Guanine Nucleotides; D015221:Potassium Channels; D013873:Thionucleotides; D006153:Guanosine Diphosphate; C046783:11,12-epoxy-5,8,14-eicosatrienoic acid; C023427:guanosine 5'-O-(2-thiodiphosphate); D002772:Cholera Toxin; D019204:GTP-Binding Proteins; D015126:8,11,14-Eicosatrienoic Acid; D002118:Calcium