IS THE CANNABINOID CB1 RECEPTOR A 2-ARACHIDONOYLGLYCEROL RECEPTOR - STRUCTURAL REQUIREMENTS FOR TRIGGERING A CA2-15 CELLS( TRANSIENT IN NG108)

The effects of Delta(9)-tetrahydrocannabinol and 2-arachidonoylglycero l on the intracellular free Ca2+ concentration ([Ca2+] (i)) in NG108-1 5 cells were examined in detail, We found that Delta(9)-tetrahydrocann abinol induces a rapid, modest increase in [Ca2+](i). The response was detectable with 3 nM Delta(9)-tetrahydrocannabinol. We also found tha t very low concentrations of 2-arachidonoylglycerol elicit a rapid, mo re prominent increase in [Ca2+](i). Such a response was observed not o nly in NG108-15 cells but also in N18TG2 cells, The response induced b y 2-arachidonoylglycerol in either NG108-15 cells or N18TG2 cells was abolished by pretreatment of the cells with a cannabinoid CB1 receptor -specific antagonist, SR141716A, suggesting that 2-arachidonoylglycero l interacts with the CB1 receptor to induce the response, The results of an experiment involving a phospholipase C inhibitor suggested that phospholipase C is involved in the rapid increase in [Ca2+](i) induced by 2-arachidonoylglycerol. We also found that 1(3)-arachidonoylglycer ol exhibits similar activity to that of 2-arachidonoylglycerol, althou gh its activity at low concentrations was somewhat weak compared with that of 2-arachidonoylglycerol. We further confirmed that several stru ctural analogues of 2-arachidonoylglycerol were less active compared w ith 2-arachidonoylglycerol. These results suggest that the structure o f 2-arachidonoylglycerol is strictly recognized by the CB1 receptor, w hich raises the possibility that the CB1 receptor is originally a 2-ar achidonoylglycerol receptor.