Lanthanides stimulate [H-3]tyramine binding in the rat striatum

Low (up to 100 nM) and high (approximate to 100 mu M) concentrations of lan thanides and Ca2+-ions, respectively, stimulated [H-3]tyramine binding ([H- 3]TY) to rat striatal membranes, a putative marker for the vesicular transp orter of dopamine. On the other hand, lanthanides (approximate to 100 mu M) inhibited or stimulated TY binding in striatal and extrastriatal (cortex, cerebellum) tissues, respectively. The binding increases by lanthanum (La3) appeared to depend on endogenous Ca2+, whereas, those induced in EDTA-pre treated membranes were Ca2+-independent. The La3+-induced, apparent increas e in the B-max for [H-3]TY binding seemed to reflect a retarded rate of dis sociation of the ligand from its targets, rather than a larger availability of functionally-relevant, vesicular transport-related TY sites. This indic ates uncertain mechanisms of present La3+ effects. (C) 1999 Elsevier Scienc e Ireland Ltd. All rights reserved.