MUSCARINIC M(2) RECEPTOR SYNTHESIS - STUDY OF RECEPTOR TURNOVER WITH PROPYLBENZILYLCHOLINE MUSTARD

We have investigated the rate and the functional responsiveness of the newly synthesised M(2) muscarinic receptors in HEL 299 cells followin g propylbenzilylcholine mustard treatment at 37 degrees C. Propylbenzi lylcholine mustard induced a dose-dependent loss of the hydrophilic li gand [H-3]N-methylscopoiamine binding sites with 80% inactivation at 0 .1 mu M. The rate of muscarinic receptor synthesis in these cells, est imated from wash-out experiments following propylbenzilylcholine musta rd treatment, was very slow and returned to control values after 36 h of propylbenzilylcholine mustard removal. The recovery of muscarinic r eceptors was blocked by the cycloheximide pre-treatment, indicating th e synthetic pathway for the new receptors. In control cells as well as in cells treated with propylbenzilylcholine mustard and allowed to re cover for 12 h, carbachol still inhibited forskolin-induced cAMP accum ulation. These results show that (i) the rate of M(2) muscarinic recep tor synthesis is slow (ii) the recovery of receptors is mainly through increased synthesis and (iii) the newly synthesised receptors retain their full functional activity.