Antagonism of an adenosine/ATP receptor in follicular Xenopus oocytes.
J PHARMACOL EXP THER
1005 - 1011.
Follicular Xenopus oocytes possess a novel receptor where both adenosine and ATP activate a cAMP-dependent, nonrectifying K+-current. Five compounds, alpha,beta-methylene ATP (alpha,beta-meATP), 8-(p-sulfophenyl)theophylline (8-SPT), theophylline, 2,2'-pyridylisatogen tosylate (PIT) and suramin, were tested as antagonists of adenosine-and ATP-activated K+-currents. The descending order of activity (pIC(50) values) against adenosine responses was: alpha,beta-meATP (6.72) = 8-SPT (6.68) > theophylline (5.32) > PIT (4.58), whereas suramin was relatively inactive. The blocking actions of alpha,beta-meATP and alkylxanthine compounds were reversible with washout, whereas blockade by PIT was irreversible. These antagonists showed similar blocking activity against ATP responses, except for PIT which was more effective at ATP responses than at adenosine responses. The selectivity of antagonists was tested against cAMP-dependent K+-currents evoked by forskolin and follicle-stimulating hormone (FSH). 8-SPT and theophylline did not inhibit but instead augmented forskolin and FSH responses; this augmentation may be caused by inhibition of phosphodiesterase activity inside follicle cells. On the other hand, alpha,beta-MeATP and PIT inhibited forskolin and FSH responses; both compounds apparently are nonselective antagonists. Thus, only alkylxanthine derivatives (8-SPT and theophylline) were selective antagonists of the novel adenosine/ATP receptor in Xenopus oocytes, whereas alpha,beta-meATP and PIT were nonselective in their blocking actions and suramin was relatively inactive.
|Title:||Antagonism of an adenosine/ATP receptor in follicular Xenopus oocytes|
|Keywords:||RAT CAUDAL ARTERY, SYMPATHETIC-NERVES, PREJUNCTIONAL PURINOCEPTORS, SURAMIN ANALOGS, K+ CURRENT, ATP, INHIBITION, RESPONSES, RELEASE, SLICES|
|UCL classification:||UCL > School of Life and Medical Sciences
UCL > School of Life and Medical Sciences > Faculty of Life Sciences
UCL > School of Life and Medical Sciences > Faculty of Life Sciences > Biosciences (Division of) > Structural and Molecular Biology
UCL > School of Life and Medical Sciences > Faculty of Medical Sciences
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