Heterogeneity of high affinity nitrobenzylthioinosine binding sites in mammalian cortical membranes: multiple forms of central nervous system nucleoside transporters?

Specific binding of [3H]nitrobenzylthioinosine to cortical membranes from several mammalian species was investigated. Rat, mouse, guinea pig, and dog membranes contained an apparent single class of binding sites; there was, however, a marked species-dependent variation in their affinity for [3H]nitrobenzylthioinosine. Rabbit cortical membranes contained two classes of binding sites and the high and low affinity components were similar to those found in guinea pig and dog cortical membranes, respectively. The [3H]nitrobenzylthioinosine binding sites in rat and the low affinity sites in rabbit were atypical in that they exhibited a low affinity for dipyridamole. It is proposed that these latter sites may represent a form of the central nervous system nucleoside transport system which is less susceptible to inhibition by dipyridamole.