Anandamide initiates Ca²⁺ signaling <i>via</i> CB₂ receptor linked to phospholipase C in calf pulmonary endothelial cells

<jats:p> <jats:list list-type="explicit-label"> <jats:list-item><jats:p>The endocannabinoid anandamide has been reported to affect neuronal cells, immune cells and smooth muscle cells <jats:italic>via</jats:italic> either CB1 or CB2 receptors. In endothelial cells, the receptors involved in activating signal transduction are still unclear, despite the fact that anandamide is produced in this cell type.</jats:p></jats:list-item> <jats:list-item><jats:p>The present study was designed to explore in detail the effect of this endocannabinoid on Ca<jats:sup>2+</jats:sup> signaling in single cells of a calf pulmonary endothelial cell line.</jats:p></jats:list-item> <jats:list-item><jats:p>Anandamide initiated a transient Ca<jats:sup>2+</jats:sup> elevation that was prevented by the CB2 receptor antagonist SR144528, but not by the CB1 antagonist SR141716A. These data were confirmed by molecular identification of the bovine CB2 receptor in these endothelial cells by partial sequencing.</jats:p></jats:list-item> <jats:list-item><jats:p>The phospholipase C inhibitor 1‐[6‐[[(17<jats:italic>β</jats:italic>)‐3‐methoxyestra‐1,3,5(10)‐trien‐17‐yl]amino]hexyl]‐1<jats:italic>H</jats:italic>‐pyrrole‐2,5dione and the inositol 1,4,5‐trisphosphate receptor antagonist 2‐aminoethoxydiphenylborate prevented Ca<jats:sup>2+</jats:sup> signaling in response to anandamide.</jats:p></jats:list-item> <jats:list-item><jats:p>Using an improved cameleon probe targeted to the endoplasmic reticulum (ER), fura‐2 and ratiometric‐pericam, which is targeted to the mitochondria, anandamide was found to induce Ca<jats:sup>2+</jats:sup> depletion of the ER accompanied by the activation of capacitative Ca<jats:sup>2+</jats:sup> entry (CCE) and a transient elevation of mitochondrial Ca<jats:sup>2+</jats:sup>.</jats:p></jats:list-item> <jats:list-item><jats:p>These data demonstrate that anandamide stimulates the endothelial cells used in this study <jats:italic>via</jats:italic> CB2 receptor‐mediated activation of phospholipase C, formation of inositol 1,4,5‐trisphosphate, Ca<jats:sup>2+</jats:sup> release from the ER and subsequent activation of CCE. Moreover, the cytosolic Ca<jats:sup>2+</jats:sup> elevation was accompanied by a transient Ca<jats:sup>2+</jats:sup> increase in the mitochondria. Thus, in addition to its actions on smooth muscle cells, anandamide also acts as a powerful stimulus for endothelial cells.</jats:p></jats:list-item> </jats:list> </jats:p><jats:p><jats:italic>British Journal of Pharmacology</jats:italic> (2003) <jats:bold>140</jats:bold>, 1351–1362. doi:<jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" xlink:href="10.1038/sj.bjp.0705529">10.1038/sj.bjp.0705529</jats:ext-link></jats:p>