The extracellular regulated kinases (ERK) 1/2 mediate cannabinoid‐induced inhibition of gap junctional communication in endothelial cells

Abstract

Cannabinoids are potent inhibitors of endothelium‐derived hyperpolarizing factor (EDHF)‐mediated relaxations. We set out to study the mechanism underlying this effect and the possible role of cannabinoid‐induced changes in intercellular gap junction communication. In cultured endothelial cells, Δ⁹‐tetrahydrocannabinol (Δ⁹‐THC) and the cannabinoid receptor agonist HU210, increased the phosphorylation of extracellular regulated kinases 1/2 (ERK1/2) and inhibited gap junctional communication, as determined by Lucifer Yellow dye transfer and electrical capacity measurements. Δ⁹‐THC elicited a pronounced increase in the phosphorylation of connexin 43, which was sensitive to PD98059 and U0126, two inhibitors of ERK1/2 activation. Inhibition of ERK1/2 also prevented the Δ⁹‐THC‐induced inhibition of gap junctional communication. Δ⁹‐THC prevented both the bradykinin‐induced hyperpolarization and the nitric oxide and prostacyclin‐independent relaxation of pre‐contracted rings of porcine coronary artery. These effects were prevented by PD98059 as well as U0126. In the absence of Δ⁹‐THC, neither PD98059 nor U0126 affected 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^ωnitro‐L‐arginine were present. Moreover, PD98059 and U0126 prolonged the bradykinin‐induced hyperpolarization of porcine coronary arteries, without affecting the magnitude of the response. 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 Δ⁹‐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. British Journal of Pharmacology (2002) 136, 709–716; doi:10.1038/sj.bjp.0704776