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Effect of 5′‐( N ‐Ethylcarboxamido)adenosine on Adenosine Transport in Cultured Chromaffin Cells
Author(s) -
Delicado Esmerilda G.,
Rodrigues Alexandra,
Sen Raquel P.,
Sebastiao Ana M.,
Ribeiro J. Alexandre,
MirasPortugal M. Teresa
Publication year - 1990
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.1471-4159.1990.tb04895.x
Subject(s) - adenosine , nucleoside transporter , adenosine receptor , nucleoside , agonist , medicine , adenosine a1 receptor , endocrinology , xanthine , forskolin , receptor , ligand (biochemistry) , chemistry , biology , transporter , biochemistry , enzyme , gene
Extracellular adenosine is transported into chromaffin cells by a high‐affinity transport system. The action of adenosine receptor ligands was studied in this cellular model 5‐( N ‐Ethylcarboxamido)adenosine (NECA), an agonist receptors, activated adenosine transport. K m values for adenosine were 4.6 ± 1.0 (n = 5) and 10.2 ± 3.0 μ M (n = 5) for controls and 100 n M NECA, respectively. The V max values were 66.7 ± 23.5 and 170.2 ± 30 pmol/10 6 cells/min for control and 100 n M NECA, respectively. The A 1 agonist N 6 ‐cyclohexyladenosine, the A 1 antagonist 8‐cyclopentyl‐1, 3‐dipropylxanthine, and the A 1 ‐A 2 antagonist 1,3‐dipropyl‐8‐{4‐[(2‐aminoethyl)amino]‐carbonylmethyloxyphenyl}‐xanthine did not significantly modify the adenosine transport in this system. Binding studies done with [ 3 H]dipyridamole, a nucleoside transporter ligand, did not show changes in either the number or affinity of transporter sites after NECA treatment. This ligand can enter cells and quantifies the total number of transporters. The binding studies with [ 3 H]‐nitrobenzylthioinosine, which quantifies the plasma membrane transporters, showed a B max of 19,200 ± 800 and 23,200 ± 700 transporters/cell for controls and 100 n M NECA, repectively. No changes in the K D were obtained. The effects of NECA were not mediated through adenylate cyclase activation, because its action was not imitated by forskolin.