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Adenosine Release and Uptake in Cerebellar Granule Neurons Both Occur via an Equilibrative Nucleoside Carrier that Is Modulated by G Proteins
Author(s) -
Sweeney M. I.
Publication year - 1996
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 - 10.1046/j.1471-4159.1996.67010081.x
Subject(s) - adenosine , nucleoside , nucleoside transporter , granule (geology) , cholera toxin , chemistry , pertussis toxin , depolarization , biophysics , biochemistry , pharmacology , biology , endocrinology , transporter , g protein , signal transduction , paleontology , gene
There is debate about the mechanisms mediating adenosine release from neurons. In this study, the release of adenosine evoked by depolarizing cultured cerebellar granule neurons with 50 m M K + was inhibited by 49 ± 7% in Ca 2+ ‐free medium. The remaining release was blocked by dipyridamole (IC 50 = 6.4 × 10 −8 M ) and nitrobenzylthioinosine (IC 50 = 3.6 × 10 −8 M ), inhibitors of adenosine uptake. Ca 2+ ‐dependent release was reduced by 78 ± 9% following a 21‐h pretreatment of the cells with pertussis toxin, which ADP‐ribosylates G i /G o G proteins, thereby preventing their dissociation. The nucleoside transporter‐mediated component of K + ‐induced adenosine release also was inhibited by 62 ± 8% by pertussis toxin and was potentiated by 78 ± 11% following cholera toxin treatment, which permanently activates G s . Uptake of [ 3 H]adenosine into cultured cerebellar granule neurons over a 10‐min period was not dependent on extracellular Na + but was reduced by dipyridamole (IC 50 = 3.2 × 10 −8 M ) and nitrobenzylthioinosine (IC 50 = 2.6 × 10 −8 M ). Thus, adenosine uptake likely occurs via the same transporter mediating Ca 2+ ‐independent adenosine release. Adenosine uptake was potentiated by cholera toxin pretreatment (152 ± 15% of control), but pertussis toxin had no statistically significant effect. It is possible that G s , G i /G o , or free Gβγ dimer modulate the equilibrative, inhibitor‐sensitive nucleoside carrier to enhance adenosine transport.