Epoxyeicosatrienoic acids, potassium channel blockers and endothelium‐dependent hyperpolarization in the guinea‐pig carotid artery

Using intracellular microelectrodes, we investigated the effects of 17‐octadecynoic acid (17‐ODYA) on the endothelium‐dependent hyperpolarization induced by acetylcholine in the guinea‐pig isolated internal carotid artery with endothelium. In the presence of N ω ‐nitro‐ L ‐arginine ( L ‐NOARG, 100 μ M ) and indomethacin (5 μ M ) to inhibit nitric oxide synthase and cyclo‐oxygenase, acetylcholine (1 μ M ) evoked an endothelium‐dependent hyperpolarization which averaged −16.4 mV starting from a resting membrane potential of −56.8 mV. There was a negative correlation between the amplitude of the hyperpolarization and the absolute values of the resting membrane potential. The acetylcholine‐induced endothelium‐dependent hyperpolarization was not altered by charybdotoxin (0.1 μ M ) or iberiotoxin (30 n M ). It was partially but significantly reduced by apamin (0.5 μ M ) to −12.8±1.2 mV ( n =10) or the combination of apamin plus iberiotoxin (−14.3±3.4 mV, n =4). However, the combination of charybdotoxin and apamin abolished the hyperpolarization and under these conditions, acetylcholine evoked a depolarization (+7.1±3.7 mV, n =8). 17‐ODYA (10 μ M ) produced a significant hyperpolarization of the resting membrane potential which averaged −59.6 mV and a partial but significant inhibition of the acetylcholine‐induced endothelium‐dependent hyperpolarization (−10.9 mV). Apamin did not modify the effects of 17‐ODYA but in the presence of charybdotoxin or iberiotoxin, 17‐ODYA no longer influenced the resting membrane potential or the acetylcholine‐induced hyperpolarization. When compared to solvent (ethanol, 1% v/v), epoxyeicosatrienoic acids (EpETrEs) (5,6‐, 8,9‐, 11,12‐ and 14,15‐EpETrE, 3 μ M ) did not affect the cell membrane potential and did not relax the guinea‐pig isolated internal carotid artery. These results indicate that, in the guinea‐pig internal carotid artery, the involvement of metabolites of arachidonic acid through the cytochrome P 450 pathway in endothelium‐dependent hyperpolarization is unlikely. Furthermore, the hyperpolarization mediated by the endothelium‐derived hyperpolarizing factor (EDHF) is probably not due to the opening of BK Ca channels.British Journal of Pharmacology (1998) 123 , 574–580; doi: 10.1038/sj.bjp.0701629