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

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 mu M) 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 mu M barium plus 500 nM ouabain depolarized intact artery smooth muscle but responses to substance P and bradykinin were unchanged. 500 mu M 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 pia myoendothelial gap junctions but the involvement of an unknown endothelial factor cannot be excluded.