Role of gap junctions and EETs in endothelium-dependent hyperpolarization of porcine coronary artery

Abstract

1. The effects of endothelium-derived hyperpolarizing factor (EDHF: elicited using substance P or bradykinin) were compared with those of 11,12-EET in pig coronary artery. Smooth muscle cells were usually impaled with microelectrodes through the adventitial surface. 2. Substance P (100 nM) and 11,12-EET (11,12-epoxyeicosatrienoic acid; 3 μM) hyperpolarized endothelial cells in intact arteries. These actions were unaffected by 100 nM iberiotoxin but were abolished by charybdotoxin plus apamin (each 100 nM). 3. Substance P (100 nM) and bradykinin (30 nM) hyperpolarized intact artery smooth muscle; Substance P had no effect after endothelium removal. 4. 11,12-EET hyperpolarized de-endothelialized vessels by 12.6 ± 0.3 mV, an effect abolished by 100 nM iberiotoxin. 11,12-EET hyperpolarized intact arteries by 18.6 ± 0.8 mV, an action reduced by iberiotoxin, which was ineffective against substance P. Hyperpolarizations to 11,12-EET and substance P were partially inhibited by 100 nM charybdotoxin and abolished by further addition of 100 nM apamin. 5. 30 μM barium plus 500 nM ouabain depolarized intact artery smooth muscle but responses to substance P and bradykinin were unchanged. 500 μM gap 27 markedly reduced hyperpolarizations to substance P and bradykinin which were abolished in the additional presence of barium plus ouabain. 6. Substance P-induced hyperpolarizations of smooth muscle cells immediately below the internal elastic lamina were unaffected by gap 27, even in the presence of barium plus ouabain. 7. In pig coronary artery, 11,12-EET is not EDHF. Smooth muscle hyperpolarizations attributed to 'EDHF' are initiated by endothelial cell hyperpolarization involving charybdotoxin- (but not iberiotoxin) and apamin-sensitive K + channels. This may spread electrotonically via myoendothelial gap junctions but the involvement of an unknown endothelial factor cannot be excluded.