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Treatment with N‐ethylmaleimide selectively reduces adenosine receptor‐mediated decreases in cyclic AMP accumulation in rat hippocampal slices
Author(s) -
Fredholm Bertil B.,
Lindgren Eva,
Lindström Karin
Publication year - 1985
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1985.tb08922.x
Subject(s) - n ethylmaleimide , forskolin , adenosine , hippocampal formation , gtp' , stimulation , receptor , medicine , binding site , chemistry , guanine , adenosine receptor , endocrinology , membrane , biophysics , biochemistry , biology , nucleotide , enzyme , agonist , gene
1 N‐ethylmaleimide (NEM) has been reported to interact with the GTP‐binding N i ‐protein; we have examined its effect on adenosine receptor binding in feline cortical membranes and on adenosine‐receptor mediated effects on cyclic AMP accumulation in rat hippocampal slices. 2 Treatment of cortical membranes with NEM (100 μM for 5 min) altered the binding of [ 3 H]‐phenylisopropyladenosine (PIA) from being almost exclusively to a single class of high affinity sites ( K D = 1.65 nM) to binding at two classes of sites ( K DH = 2.1 nM, K DL = 102 nM). The total number of binding sites was similar (825–845 fmol mg −1 in control membranes, 944–1428 fmol mg −1 in NEM‐treated membranes). 3 In rat hippocampal slices treated with forskolin (0.3 μM) L‐PIA produced a biphasic effect on cyclic AMP accumulation: an inhibition at 0.03 to 1 μM and at higher concentrations, a stimulation. Treatment with 50 μM NEM selectively inhibited the inhibitory phase, causing stimulation at lower concentrations of L‐PIA. At 50 μM, NEM did not alter basal or forskolin‐stimulated cyclic AMP accumulation but at higher concentrations inhibition was observed. 4 It is concluded that NEM can, in certain doses, selectively block adenosine A 1 ‐receptor‐mediated effects without affecting A 2 ‐receptor‐mediated actions in the same tissue. It is suggested that this is due to NEM affecting the N i guanine nucleotide binding protein.