Carrier-mediated transport and enzymatic hydrolysis of the endogenous cannabinoid 2-arachidonylglycerol

The human astrocytoma cell line CCF-STTG1 accumulates [H-3]2-AG through an Na+- and energy-independent process, with a K-m of 0.7 +/- 0.1 mu M. Non-radioactive 2-AG, anandamide or the anandamide transport inhibitor 4-hydroxyphenyl arachidonamide inhibit [H-3]2-AG uptake with half-maximal inhibitory concentrations (IC50) of 5.5 +/- 1.0 mu M, 4.2 +/- 0.3 mu M and 1.8 +/- 0.1 mu M, respectively. A variety of lipid transport substrates and inhibitors interfere with neither [H-3]2-AG nor [H-3]anandamide uptake. These results suggest that 2-AG and anandamide are internalized in astrocytoma cells through a common carrier-mediated mechanism. After incubation with [H-3]2-AG, radioactivity is recovered in phospholipids, monoacylglycerols (unmetabolized [H-3]2-AG), free fatty acids ([H-3]arachidonate) and, to a minor extent, diacylglycerols and triacylglycerols. Arachidonic acid (100 mu M) and triacsin C (10 mu M), an acyl-CoA synthetase inhibitor, prevent incorporation of [H-3]arachidonic acid in phospholipids and significantly reduce [H-3]2-AG transport. Thus, the driving force for 2-AG internalization may derive from the hydrolysis of 2-AG to arachidonate and the subsequent incorporation of this fatty acid into phospholipids. NeuroReport 11:1231-1235 (C) 2000 Lippincott Williams & Wilkins.