Human brain endothelium: Coexpression and function of vanilloid and endocannabinoid receptors

The arachidonic acid derivative, 2-arachidonoyl-glycerol (2-AG), was initially isolated from gut and brain; it is also produced and released from blood and vascular cells. Many of the 2-AG-induced cellular responses (i.e., neuromodulation, cytoprotection and vasodilation) are mediated by cannabinoid receptors CB ₁ and CB ₂. The findings presented here demonstrate the expression of CB ₁, CB ₂ and TRPV1 receptors on cerebromicrovascular endothelial cells (HBEC). The expression of TRPV1, CB ₁ and CB ₂ receptor mRNA and proteins were demonstrated by RT-PCR and polyclonal antibodies, respectively. The endocannabinoid 2-AG, and other related compounds [anandamide (ANA), methanandamide (m-ANA), N-(4-hydroxyphenyl-arachidonyl-ethanolamide) (AM404) and capsaicin] dose-dependently stimulated Ca ²⁺ influx in HBEC. The selective TRPV1 receptor antagonist (capsazepine), CB ₁ receptor antagonist (SR141716A) and CB ₂ receptor antagonist (SR144528) inhibited these responses. The effects of capsaicin, a specific agonist for TRPV1 receptors, were inhibited by capsazepine, but only weakly by CB ₁ or CB ₂ receptor antagonists. 2-AG also induced phosphorylation of vasodilator-stimulated phosphoprotein (VASP); this response was mediated by VR1 receptors. These studies clearly indicate that 2-AG and other related compounds may function as agonists on VR1 receptors, as well as CB ₁ and CB ₂ receptors, and implicated these factors in various HBEC functions.