Binding of [ 3 H]phencyclidine to membranes from housefly thoracic muscles

The binding of [ 3 H]phencyclidine ([ 3 H]PCP) to a preparation of housefly thoracic muscle membranes was studied. Specific [ 3 H]PCP binding saturated with both time and at concentrations of the radiolabeled ligand greater than 20 nM. One binding site with a K D of 10.7 nM and a B max of 3.9 pmol/mg protein was observed. Specific [ 3 H]PCP binding was also readily reversible with a half‐time of dissociation (t 1/2 ) of 13.8 min and varied proportionately with tissue concentration. Of the drugs tested, specific [ 3 H]PCP binding was inhibited by PCP analogs, antipsychotics, antidepressants, Ca 2+ channel antagonists, and K + channel blockers. [ 3 H]PCP binding was unaffected by addition of carbamylcholine or L‐glutamate in absence or presence of ATP, GTP, cAMP, or cGMP. Though the identity of the [ 3 H]PCP binding protein in housefly muscle membranes is still unclear, it is more likely to be an ionic channel such as K + or Ca 2+ channels than a neurotransmitter receptor.