It is not yet clear if the endocannabinoid 2-arachidonoyl-glycerol (2-AG) is transported into cells through the same membrane transporter mediating the uptake of the other endogenous cannabinoid, anandamide (N-arachidonoyl-ethanolamine, AEA), and whether this process (a) is regulated by cells and (b) limits 2-AG pharmacological actions. We have studied simultaneously the facilitated transport of [14C]AEA and [3H]2-AG into rat C6 glioma cells and found uptake mechanisms with different efficacies but similar affinities for the two compounds (Km 11.0 ± 2.0 and 15.3 ± 3.1 μ, Bmax 1.70 ± 0.30 and 0.24 ± 0.04 nmol·min-1·mg protein-1, respectively). Despite these similar Km values, 2-AG inhibits [14C]AEA uptake by cells at concentrations (Ki ± 30.1 ± 3.9 μ) significantly higher than those required to either 2-AG or AEA to inhibit [3H]2-AG uptake (Ki ± 18.9 ± 1.8 and 20.5 ± 3.2 μ, respectively). Furthermore: (a) if C6 cells are incubated simultaneously with identical concentrations of [14C]AEA and [3H]2-AG, only the uptake of the latter compound is significantly decreased as compared to that observed with [3H]2-AG alone; (b) the uptake of [14C]AEA and [3H]2-AG by cells is inhibited with the same potency by AM404 (Ki ± 7.5 ± 0.7 and 10.2 ± 1.7 μ, respectively) and linvanil (Ki ± 9.5 ± 0.7 and 6.4 ± 1.2 μ, respectively), two inhibitors of the AEA membrane transporter; (c) nitric oxide (NO) donors enhance the uptake of both [14C]AEA and [3H]2-AG, thus suggesting that 2-AG action can be regulated through NO release; (d) AEA and 2-AG induce a weak release of NO that can be blocked by a CB1 cannabinoid receptor antagonist, and significantly enhanced in the presence of AM404 and linvanil, thus suggesting that transport into C6 cells limits the action of both endocannabinoids.
- Nitric oxide
ASJC Scopus subject areas