Receptor-independent depression of DA and 5-HT uptake by cannabinoids in rat neocortex--involvement of Na(+)/K(+)-ATPase.
There is evidence that cannabinoids modulate the reuptake of some neurotransmitters in the central nervous system. In this study, we investigated the effects of the synthetic cannabinoid receptor agonist WIN55212-2, the endocannabinoid anandamide and the chemically related arachidonic acid on serotonin (5-HT) and dopamine (DA) uptake into rat neocortical synaptosomes. At micromolar concentrations, anandamide and arachidonic acid produced steep inhibition curves with Hill coefficients above unity. WIN55212-2 inhibited both DA and 5-HT uptake with Hill coefficients near unity, also within the micromolar range. The effect of WIN55212-2 was not mediated by cannabinoid receptors, since the CB1 receptor antagonist AM251 failed to diminish uptake inhibition by WIN55212-2 and since the Ki estimates of WIN55212-2 were outside the range of the dissociation constants of WIN55212-2 at both CB1 and CB2 receptors. A 100-fold higher concentration of DA, respectively 5-HT, did not induce a shift to the right of the WIN55212-2 concentration-inhibition curves, suggesting a carrier-independent mechanism. The Na(+)/K(+)-ATPase inhibitor ouabain concentration dependently inhibited 5-HT uptake. Possible drug effects on commercial Na(+)/K(+)-ATPase and synaptosomal ATP consumption were investigated using an ATP bioluminescence assay. Ouabain inhibited both commercial and synaptosomal Na(+)/K(+)-ATPase. WIN55212-2 had no effect on commercial Na(+)/K(+)-ATPase, but inhibited synaptosomal ATP consumption. Anandamide produced a sharp decrease in the activity of commercial Na(+)/K(+)-ATPase and on synaptosomal ATP consumption. Presence of ouabain significantly reduced the inhibitory effect of anandamide on synaptosomal ATP consumption, whereas the effect of WIN55212-2 remained unchanged. Our results show that cannabinoids and arachidonic acid inhibit DA and 5-HT uptake into rat neocortical synaptosomes. This effect is neither cannabinoid receptor-mediated nor due to competitive inhibition of membrane transporters, but is partly effected by a decreased Na(+)/K(+)-ATPase activity.
Steffens
Marc
M
Sektion Klinische Neuropharmakologie der Neurologischen Universitätsklinik, Neurozentrum, Breisacher Strasse 64, D-79106 Freiburg, Germany.
Feuerstein
Thomas J
TJ
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D016718:Arachidonic Acid / Q000494:pharmacology; D048588:Benzoxazines; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002186:Cannabinoids / Q000494:pharmacology*; D002794:Choline / Q000378:metabolism; D004298:Dopamine / Q000378:metabolism*; D018765:Dopamine Uptake Inhibitors / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D008156:Luciferases / Q000378:metabolism; D008163:Luminescent Measurements; D008297:Male; D009025:Morpholines / Q000494:pharmacology; D009281:Naphthalenes / Q000494:pharmacology; D019579:Neocortex / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D051381:Rats; D043884:Receptor, Cannabinoid, CB1 / Q000187:drug effects; D012701:Serotonin / Q000378:metabolism*; D017367:Selective Serotonin Reuptake Inhibitors / Q000494:pharmacology*; D012967:Sodium Dodecyl Sulfate / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism
D000255:Adenosine Triphosphate; D016718:Arachidonic Acid; D048588:Benzoxazines; D002121:Calcium Channel Blockers; D002186:Cannabinoids; D002794:Choline; D004298:Dopamine; D018765:Dopamine Uptake Inhibitors; D004791:Enzyme Inhibitors; D008156:Luciferases; D009025:Morpholines; D009281:Naphthalenes; D010042:Ouabain; D043884:Receptor, Cannabinoid, CB1; D012701:Serotonin; D017367:Selective Serotonin Reuptake Inhibitors; D012967:Sodium Dodecyl Sulfate; D000254:Sodium-Potassium-Exchanging ATPase; C070417:(3R)-((2,3-dihydro-5-methyl-3-((4-morpholinyl)methyl)pyrrolo-(1,2,3-de)-1,4-benzoxazin-6-yl)(1-naphthalenyl))methanone