A comparative study of binding sites for diisopropyl phosphorofluoridate in membrane and cytosol preparations from spinal cord and brain of hens

Biochemical events in the initiation of organophosphorus induced delayed ne urotoxicity (OPIDN) are not well understood To find new putative target(s) for OPIDN, rye investigated the biochemical and pharmacological characteris tics of [H-3]diisopropyl phosphorofluoridate (DFP) binding to membrane and cytosol preparations from the brain and spinal cold of hens in vitro. [H-3] DFP binding to both preparations was determined by the specific binding obt ained by subtracting non-specific binding from total binding. The specific binding sites of [H-3]DFP were found not only on membrane but also in cytos ol. K-d values were higher and B-max values were lower in cytosol than in m embrane. Moreover; the Kd values in both membrane and cytosol preparations from spinal cord were lower than those of brain. The B-max values in membra ne and cytosol were similar between brain and spinal cord. The specific bin ding to both preparations was markedly displaced by unlabeled DFP. The spec ific binding of DFP to the membrane was highly or partly displaced by organ ophosphorus compounds (OPs) or a carbamate, respectively. However both the OPs and the carbanmate had considerably weaker blocking effects on the spec ific binding of DFP to cytosol. Noire of the compounds known to interact wi th neuropathy target esterase (NTE) had a strong blocking effect on the spe cific binding of DFP to either membrane or cytosol. These results show that the specific binding of DFP to the membrane may be binding with cholineste rase (ChE). However; cytosol, especially in spinal cord, may have DFP bindi ng sites other than ChE and NTE. (C) 2001 Elsevier Science Inc. All rights reserved.