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Heterogeneity of [ 3 H]Dipyridamole Binding to CNS Membranes: Correlation with [ 3 H]Nitrobenzylthioinosine Binding and [ 3 H]Uridine Influx Studies
Author(s) -
Jones K. W.,
Hammond J. R.
Publication year - 1992
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1992.tb08449.x
Subject(s) - nucleoside transporter , nucleoside , dipyridamole , chemistry , membrane transport , binding site , adenosine , membrane , uridine , synaptosome , guinea pig , biochemistry , biophysics , transporter , biology , medicine , endocrinology , rna , gene
Abstract: The relationship between the nucleoside transport system and the nitrobenzylthioinosine‐sensitive and ‐resistant [ 3 H]dipyridamole binding sites was examined by comparing the characteristics of [ 3 H]dipyridamole binding with those of [ 3 H]nitrobenzylthioinosine binding and [ 3 H]‐uridine influx in rabbit and guinea pig cerebral cortical synaptosomes. Two distinct high‐affinity synaptosomal membrane‐associated [ 3 H]dipyridamole binding sites, with different sensitivities to inhibition by nitrobenzylthioinosine, were characterized in the presence of 3–[(3‐cholamidopropyl)dimethylammonio]‐1 ‐propanesulfonate (CHAPS, 0.01%) to prevent [ 3 H]dipyridamole binding to glass tubes and niters. The nitrobenzylthioinosine‐resistant [ 3 H]‐dipyridamole binding sites represented a greater proportion of the total membrane sites in guinea pig than in rabbit (40 vs. 10% based on inhibition studies). In rabbit, nitrobenzylthioinosine‐sensitive [ 3 H]dipyridamole binding ( K D = 1.4 ± 0.2 n M ) and [ 3 H]nitrobenzylthioinosine binding ( K D = 0.30 ± 0.01 n M ) appeared to involve the same membrane site associated with the nitrobenzylthioinosine‐sensitive nucleoside transporter. By mass law analysis, [ 3 H]‐dipyridamole binding in guinea pig could be resolved into two components based on sensitivity to inhibition by 1 μ M nitrobenzylthioinosine. The nitrobenzylthioinosine‐resistant [ 3 H]dipyridamole binding sites were relatively insensitive to inhibition by all of the nucleoside transport substrates and inhibitors tested, with the exception of dipyridamole itself. In guinea pig synaptosomes, 100 μ M dilazep blocked nitrobenzylthioinosine‐resistant [ 3 H]uridine transport completely but inhibited the nitrobenzylthioinosine‐resistant [ 3 H]dipyridamole binding component by only 20%. Furthermore, a greater percentage of the [ 3 H]‐dipyridamole binding was nitrobenzylthioinosine resistant in guinea pig compared with rabbit, yet both species had a similar percentage of nitrobenzylthioinosine‐resistant [ 3 H]‐uridine transport. These data suggest that the nitrobenzylthioinosine‐resistant [ 3 H]dipyridamole binding site(s) involves membrane components distinct from those associated with functional, nitrobenzylthioinosine‐resistant, nucleoside transporters.