Bradykinin-induced, endothelium-dependent responses in porcine coronary arteries:: involvement of potassium channel activation and epoxyeicosatrienoic acids

1 In coronary arteries, bradykinin opens endothelial intermediate- and small-conductance Ca2+-sensitive K+ channels (IKCa and SKCa) and, additionally, releases epoxyeicosatrienoic acids (EETs) from the endothelium. To clarify the involvement of these pathways in endothelium-dependent myocyte hyperpolarization, bradykinin-induced electrical changes in endothelial cells and myocytes of porcine coronary arteries ( following nitric oxide ( NO) synthase and cyclooxygenase inhibition) were measured using sharp microelectrodes. 2 Hyperpolarization of endothelial cells by bradykinin (27.0 +/- 0.9 mV, n = 4) was partially inhibited (74%) by blockade of IKCa and SKCa channels using 10 mu M TRAM-39 (2-(2-chlorophenyl)-2,2-diphenylacetonitrile) plus 100 nM apamin ( leaving an iberiotoxin-sensitive component), whereas the response to substance P was abolished. 3 After gap junction blockade with HEPES, (N-(2-hydroxyethyl)piperazine-N'-(2-ethanesulphonic acid)) hyperpolarization of the endothelium by 100 nM bradykinin was abolished by TRAM- 39 plus apamin, whereas myocyte hyperpolarization still occurred (12.9 +/- 1.0 mV, n = 4). The residual hyperpolarizations to 100 nM bradykinin were antagonized by the EET antagonist, 14,15-EEZE (14,15-epoxyeicosa-5(Z)-enoic acid) (10 mu M), and abolished by iberiotoxin. Bradykinin-induced myocyte hyperpolarizations were also reduced by 14,15-EEZE-mSI (14,15-EEZE-methylsulfonylimide) (5,6- and 14,15-EET antagonist), whereas those to exogenous 11,12-EET were unaffected. 4 These data show that bradykinin-induced hyperpolarization of endothelial cells ( due to the opening of IKCa and SKCa channels) is electrotonically transferred to the myocytes via gap junctions. Bradykinin ( but not substance P) also hyperpolarizes myocytes by a mechanism ( independent of endothelial cell hyperpolarization) which involves endothelial cell production of EETs ( most likely 14,15- and/ or 11,12-EET). These open endothelial IKCa and SKCa channels and also activate large-conductance calcium-sensitive K+ channels (BKCa) on the surrounding myocytes.