Abstract

[3H]Phencyclidine ( [3H]PCP) bound to crayfish abdominal muscle membranes at pH 7.4 with two affinities (Kd of 0.96 nM for 0.38 pmole/mg of protein, and 18.9 nM for 7.6 pmoles/mg of protein). Binding affinities increased at higher pH, suggesting that binding may be due mostly to the un-ionized form of [3H]PCP. This high-affinity [3H]PCP binding was sensitive to the actions of trypsin, protease, and dicyclohexylcarbodiimide, but insensitive to phospholipase A, concanavalin A,N-ethylmaleimide, and dithiothreitol. Calcium channel antagonists were most potent in inhibiting the high-affinity [3H]PCP binding with the following descending order of potencies: bepridil greater than nicardipine = diltiazem = verapamil greater than cinnarizine greater than (+)-D-600 greater than (-)-D-600 greater than 4-NO2-nifedipine greater than 2-NO2-nifedipine. The binding was also highly sensitive to several PCP analogues, antipsychotics, piperocaine , and tilorone, and moderately sensitive to d-tubocurarine, atropine, imipramine, nortryptyline , and tetracaine. Although verapamil and nifedipine inhibited the action potential of crayfish muscle, PCP did not and actually prolonged slightly the falling phase of the action potential. Although it is unlikely that the [3H]PCP binding protein in crayfish muscles is a Ca2+ channel, it is possible that it may be a K+ channel.