Arg-Lys-Asp-Val-Tyr (thymopentin) accelerates the cholinergic-induced inactivation (desensitization) of reconstituted nicotinic receptor.

1. The thymic hormone thymopoietin blocks neuromuscular transmission and was proposed (Goldstein, 1974) as a modulator of synaptic conductivity. 2. The cholinergic-induced inactivation of nicotinic receptor reconstituted into asolectin lipid vesicles was studied in the presence and in the absence of thymopentin, a synthetic pentapeptide corresponding to positions 32-36 of thymopoietin. 3. The present data show that thymopentin accelerates desensitization of the nicotinic acetylcholine receptor, supporting the aforementioned physiological role proposed for thymopoietin. 4. They also suggest that the hormone itself and/or a yet unidentified hormine-derived peptide fragment may act as an endogenous ligand for nicotinic acetylcholine receptor desensitization.