Abstract-Functional gap junctional communication between vascular cells has been implicated in ascending dilatation and the cytochrome P-450 (CYP) inhibitor-sensitive and NO-and prostacyclin-independent dilatation of many vascular beds. Here, we assessed the mechanisms by which the epoxyeicosatrienoic acids (EETs) generated by a CYP 2C enzyme control interendothelial gap junctional communication. In CYP 2C-expressing porcine coronary endothelial cells, bradykinin, which enhances EET formation, elicited a biphasic effect on the electrical coupling and transfer of Lucifer yellow between endothelial cells, consisting of a transient increase in coupling followed by a sustained uncoupling. The initial phase was sensitive to the CYP 2C9 inhibitor sulfaphenazole and the protein kinase A (PKA) inhibitors Rp-cAMPS and KT5720 and could be mimicked by forskolin and caged cAMP as well as by the PKA activators 5,6-dichloro-1-␤-D-ribofuranosylbenzimidazole 3Ј,5Ј-cyclic monophosphorothioate sodium salt and Sp-cAMPS. Gap junction uncoupling in bradykinin-stimulated porcine coronary endothelial cells was prevented by inhibiting the activation of extracellular signal-regulated kinase (ERK)1/2. In human endothelial cells, which express little CYP 2C, bradykinin elicited only an ERK1/2-mediated inhibition of intercellular communication. The CYP 2C9 product, 11,12-EET, also exerted a dual effect on the electrical and dye coupling of human endothelial cells, which was sensitive to PKA inhibition. These results demonstrate that an agonist-activated CYP-dependent pathway as well as 11,12-EET can positively regulate interendothelial gap junctional communication, most probably via the activation of PKA, an effect that is curtailed by the subsequent activation of ERK1/2. (Circ Res. 2002;90:800-806.)Key Words: connexin43 Ⅲ cytochrome P-450 2C Ⅲ cAMP Ⅲ endothelium-derived hyperpolarizing factors Ⅲ 11,12-epoxyeicosatrienoic acid I n large arteries and veins, gap junctions are known to be essential for the propagation of electrical signals between vascular smooth muscle cells, whereas in the microcirculation they appear to be involved in the phenomena of ascending dilation and endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxation (see review 1 ).Myoendothelial gap junctions have been identified in numerous vascular beds, particularly in small arteries and terminal arterioles, 2 and it is assumed that the selective gating of such gap junctions plays an integral role in endotheliumdependent and in NO-and prostacyclin (PGI 2 )-independent relaxation. 3-6 However, there has been no convincing demonstration of a direct link between dynamic alterations in myoendothelial gap junctions and relaxation/vasodilatation.Interendothelial, rather than myoendothelial, cell communication has recently been proposed to be the pathway by which hyperpolarization and vasodilatation are conducted along agonist-stimulated resistance vessels. 7 In mice and hamsters, 8 -10 this phenomenon has been linked to a cytochrome P-450 (CYP)-dependent process t...

1 Cannabinoids are potent inhibitors of endothelium-derived hyperpolarizing factor (EDHF)-mediated relaxations. We set out to study the mechanism underlying this eect and the possible role of cannabinoid-induced changes in intercellular gap junction communication. -THC prevented both the bradykinin-induced hyperpolarization and the nitric oxide and prostacyclin-independent relaxation of pre-contracted rings of porcine coronary artery. These eects were prevented by PD98059 as well as U0126. 5 In the absence of D 9 -THC, neither PD98059 nor U0126 aected the NO-mediated relaxation of coronary artery rings but both substances induced a leftward shift in the concentration ± relaxation curve to bradykinin when diclofenac and N o nitro-L-arginine were present. Moreover, PD98059 and U0126 prolonged the bradykinin-induced hyperpolarization of porcine coronary arteries, without aecting the magnitude of the response. 6 These results indicate that the cannabinoid-induced activation of ERK1/2, which leads to the phosphorylation of connexin 43 and inhibition of gap junctional communication, may partially account for the D 9-THC-induced inhibition of EDHF-mediated relaxation. Moreover, the activation of ERK1/2 by endothelial cell agonists such as bradykinin, appears to exert a negative feedback inhibition on EDHF-mediated responses.