Effects of phenothiazines and dibenzazepines on axonal transport and microtubule assembly in vitro

Various phenothiazines (thioridazine, trifluoperazine and chlorpromazine) and dibenzazepines (lofepramine, amitriptyline and desipramine) were studied for effects on fast axonal transport (AXT) in vitro in frog sciatic nerves. AXT, measured as the accumulation of (³H) leucine‐labelled proteins in front of a ligature, was inhibited by more then 50% by all the drugs tested at 0.2 mM concentrations. Thioridazine and lofepramine were the most potent inhibitors. These effects were not due to decreased ganglionic incorporation. Some of the drugs also reduced the levels of high energy phosphates, adenosinetriphosphate (ATP) and creatinephosphate (CrP), but not to an extent which is likely to explain the arrested AXT. The polymerization of purified brain tubulin was inhibited by the phenothiazines but unaffected by the dibenzazepines at concentrations which inhibited AXT. Phenothiazines and dibenzazepines are chemically related and known to have a high affinity for calmodulin. The possibility that these drugs interefere with calmodulin regulated processes of importance for AXT will be discussed.