Immunologically distinct isoforms of ecto-5'-nucleotidase in nerve terminals of different areas of the rat hippocampus.
Ecto-5'-nucleotidase is regarded as being the key enzyme in the formation of the neuromodulator adenosine from released ATP. However, the association of ecto-5'-nucleotidase with nerve terminals is not consensual. Only enzyme histochemical and biochemical studies, but not immunocytochemical studies, agree on a general synaptic location of the enzyme. To clarify this issue further we tested the effect of an antibody against ecto-5'-nucleotidase, previously used in immunocytochemical studies, on the activity of ecto-5'-nucleotidase in fractions of nerve terminals isolated from different areas of rat hippocampus. The specific activity of extracellular AMP catabolism was higher in synaptosomes from the CA3 area (0.81+/-0.06 nmol/min/mg of protein) than from synaptosomes from the CA1 area or the dentate gyrus or from the whole hippocampus (0.49-0.68 nmol/ min/mg of protein). The catabolism of AMP (10 microM) was equally inhibited (85-92%) in synaptosomes from whole hippocampus, CA1, CA3, or dentate gyrus by alpha,beta-methylene-ADP (100 microM) and equally unaffected by p-nitrophenyl phosphate (0.5 mM) or rabbit IgGs (100 microg/ml). However, the antiserum against ecto-5'-nucleotidase (100 microg/ml) inhibited extracellular AMP catabolism by 44% in CA3 synaptosomes but had little or no effect in synaptosomes from CA1, dentate gyrus, or whole hippocampus. A similar difference in the inhibitory potential of the antibody was observed between fractions of isolated 5'-nucleotidase binding to concanavalin A-Sepharose (70%) and fractions not retained by the lectin column (18%). Taken together, these results suggest that immunological isoforms of ecto-5'-nucleotidase exist in the rat hippocampal nerve terminals, with predominance in the CA3 area.
Cunha
R A
RA
Laboratory of Neurosciences, Faculty of Medicine, University of Lisbon, Portugal. racunha@neurociencias.pt
Brendel
P
P
Zimmermann
H
H
Ribeiro
J A
JA
D015720:5'-Nucleotidase / Q000276:immunology / Q000378:metabolism*; D000241:Adenosine / Q000096:biosynthesis; D000244:Adenosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000249:Adenosine Monophosphate / Q000037:antagonists & inhibitors / Q000378:metabolism; D000818:Animals; D005110:Extracellular Space / Q000378:metabolism; D006624:Hippocampus / Q000201:enzymology*; D007106:Immune Sera / Q000494:pharmacology; D007158:Immunologic Techniques; D007527:Isoenzymes / Q000378:metabolism*; D007700:Kinetics; D009411:Nerve Endings / Q000201:enzymology* / Q000276:immunology; D011817:Rabbits; D051381:Rats; D013574:Synaptosomes / Q000378:metabolism; D014018:Tissue Distribution
D007106:Immune Sera; D007527:Isoenzymes; C523965:alpha,beta-methyleneadenosine 5'-diphosphate; D000249:Adenosine Monophosphate; D000244:Adenosine Diphosphate; D015720:5'-Nucleotidase; D000241:Adenosine