Cannabinoids inhibit sodium-dependent, high-affinity excitatory amino acid transport in cultured rat cortical astrocytes.
Cannabinoids have been shown to increase the extracellular levels of glutamate in vivo and in vitro, but no studies have evaluated the possible involvement of glial glutamate reuptake system. The present study investigates whether cannabinoids and endocannabinoid, anandamide have an effect on astroglial excitatory amino acid (EAA) transport. The kinetics of glutamate transport was studied in rat cortical astrocytes, using the radiolabeled, non-metabolized amino acid, D-[3H] aspartate in the absence or presence of cannabinoid receptor agonists. The results show that in vehicle controls the uptake of d-aspartate was rapid, sodium-dependent and saturated within the first 5 min, resulting in a K(m) 7.365+/-1.16 micromol/L (n=5) and the maximum velocity (V(max)) 1207+/-51 nmol/mg protein/min. Addition of the synthetic cannabinoid analog R(+)-[2,3-dihydro-5-methyl-3-[(morpholinyl)methyl]pyrrolol][1,2,3de]-1,4-benzoxazinyl]-(1-naphthalenyl)methanone (WIN 55,212-2; 3 micromol/L) increased the K(m) (26.25+/-4.84 micromol/L) without affecting the V(max) (1122+/-77 nmol/mg protein/min), suggesting the inhibition was competitive and reversible. Various other cannabinoid agonists also inhibited D-aspartate uptake in a dose-dependent and stereospecific manner. The cannabinoid inhibition of EAA transport was partially blocked by the cannabinoid type-1 (CB1) receptor antagonist N-(piperidin-1-yl-5(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamidehydrochloride (SR141716A; 100 nmol/L). The inhibitory effects of WIN 55,212-2, or its endogenous counterpart anandamide were reversed by 98,059, an inhibitor of mitogen-activated kinase (MAPK) kinase (MEK). These results suggest that cannabinoids and endocannabinoids may constitute a novel class of inhibitors of astroglial glutamate transport system.
Shivachar
Amruthesh C
AC
Department of Pharmaceutical Sciences, College of Pharmacy and Health Sciences, Texas Southern University, Houston, TX 77004, USA. Shivachar_AC@tsu.edu
D000818:Animals; D000831:Animals, Newborn; D001095:Arachidonic Acids / Q000494:pharmacology; D001224:Aspartic Acid / Q000378:metabolism; D001253:Astrocytes / Q000187:drug effects*; D048588:Benzoxazines / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects*; D015415:Biomarkers / Q000378:metabolism; D063386:Cannabinoid Receptor Agonists; D063385:Cannabinoid Receptor Modulators / Q000378:metabolism; D002186:Cannabinoids / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology; D003511:Cyclohexanols / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D063388:Endocannabinoids; D018846:Excitatory Amino Acids / Q000037:antagonists & inhibitors*; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D007150:Immunohistochemistry; D007700:Kinetics; D007770:L-Lactate Dehydrogenase / Q000032:analysis; D009025:Morpholines / Q000494:pharmacology; D009281:Naphthalenes / Q000494:pharmacology; D010880:Piperidines / Q000494:pharmacology; D053284:Polyunsaturated Alkamides / Q000494:pharmacology; D011506:Proteins / Q000032:analysis; D011720:Pyrazoles / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D043884:Receptor, Cannabinoid, CB1 / Q000037:antagonists & inhibitors; D000077285:Rimonabant; D012964:Sodium / Q000378:metabolism*; D013997:Time Factors
D001095:Arachidonic Acids; D048588:Benzoxazines; D015415:Biomarkers; D063386:Cannabinoid Receptor Agonists; D063385:Cannabinoid Receptor Modulators; D002186:Cannabinoids; D003511:Cyclohexanols; D063388:Endocannabinoids; D018846:Excitatory Amino Acids; D005904:Glial Fibrillary Acidic Protein; D009025:Morpholines; D009281:Naphthalenes; D010880:Piperidines; D053284:Polyunsaturated Alkamides; D011506:Proteins; D011720:Pyrazoles; D043884:Receptor, Cannabinoid, CB1; D001224:Aspartic Acid; C070417:(3R)-((2,3-dihydro-5-methyl-3-((4-morpholinyl)methyl)pyrrolo-(1,2,3-de)-1,4-benzoxazin-6-yl)(1-naphthalenyl))methanone; C054649:3-(2-hydroxy-4-(1,1-dimethylheptyl)phenyl)-4-(3-hydroxypropyl)cyclohexanol; D012964:Sodium; D007770:L-Lactate Dehydrogenase; D000077285:Rimonabant; C078814:anandamide