Arachidonic Acid Evokes an Increase in Intracellular Ca²⁺ Concentration and Nitric Oxide Production in Endothelial...

It has long been known that the conditionally essential polyunsaturated arachidonic acid (AA) regulates cerebral blood flow (CBF) through its metabolites prostaglandin E2 and epoxyeicosatrienoic acid, which act on vascular smooth muscle cells and pericytes to vasorelax cerebral microvessels. However, AA may also elicit endothelial nitric oxide (NO) release through an increase in intracellular Ca²⁺ concentration ([Ca²⁺]_i). Herein, we adopted Ca²⁺ and NO imaging, combined with immunoblotting, to assess whether AA induces intracellular Ca²⁺ signals and NO release in the human brain microvascular endothelial cell line hCMEC/D3. AA caused a dose-dependent increase in [Ca²⁺]_i that was mimicked by the not-metabolizable analogue, eicosatetraynoic acid. The Ca²⁺ response to AA was patterned by endoplasmic reticulum Ca²⁺ release through type 3 inositol-1,4,5-trisphosphate receptors, lysosomal Ca²⁺ mobilization through two-pore channels 1 and 2 (TPC1-2), and extracellular Ca²⁺ influx through transient receptor potential vanilloid 4 (TRPV4). In addition, AA-evoked Ca²⁺ signals resulted in robust NO release, but this signal was considerably delayed as compared to the accompanying Ca²⁺ wave and was essentially mediated by TPC1-2 and TRPV4. Overall, these data provide the first evidence that AA elicits Ca²⁺-dependent NO release from a human cerebrovascular endothelial cell line, but they seemingly rule out the possibility that this NO signal could acutely modulate neurovascular coupling.