Interaction of Phencyclidines with Acetylcholine Receptor in Cultured Myotubes

Several laboratories have shown that phencyclidine (PCP) and analog drugs interact with the ionic channel of the nicotinic acetylcholine receptor (AChR). These studies were done on two separate preparations, animal organs for electrophysiological studies and membrane preparations for biochemical studies. This work, however, was performed with myotubes grown in culture: these provide a convenient experimental system for the study of PCP and analog drug effects on both receptor function and receptor binding properties. Moreover, the extent of PCP retention by these cells was studied on the same preparations. All experiments were performed on viable cells in petri dishes. PCP and four PCP analogs were found to inhibit carbamylcholine induced 22Na and 45Ca ion fluxes with 50% inhibition (I50) at 2–6 μM drug concentration. The I50 for carbamylcholine induced 42K efflux was 8–20 μM. Ketamine was less efficient with an I50 of 100 μM. 125 I-α-Bungarotoxin binding was not affected at drug concentrations that cause 100% inhibition of ion fluxes. Uptake of 3H-PCP by the myotubes was a saturable process with half maximal saturation at ~ 20 μM PCP. It was inhibited by PCP and by several tertiary PCP analogs, with an I50 of ~ 20 μM. The quaternary analog PCP-methiodide (PCPMeI) however, was much less effective with an I50 of 1 mM. The capacity for 3H-PCP retention by the cells was 4 nmol/mg protein. PCPMeI was as potent as PCP in its inhibition of the AChR function although the amount retained by the cells was 50-fold lower than that of PCP. These results are consistent with the theory that PCP and analog drugs affect AChR function at a site other than the α-Bungarotoxin binding site, possibly at the ionic channel of the nicotinic receptor.