| We have recently shown that the mu opioid receptor [ MOR 1 , also termed mu opioid peptide ( MOP ) receptor ] is associated with the phospholipase D 2 ( PLD 2 ) , a phospholipid specific phosphodiesterase located in the plasma membrane . ^^^ We further demonstrated that , in human embryonic kidney ( HEK ) 293 cells co expressing MOR 1 and PLD 2 , treatment with ( D Ala 2 , Me Phe 4 , Glyol 5 ) enkephalin ( DAMGO ) led to an increase in PLD 2 activity and an induction of receptor endocytosis , whereas morphine , which does not induce opioid receptor endocytosis , failed to activate PLD 2 . ^^^ |