title: Treatment with N-ethylmaleimide selectively reduces adenosine receptor-mediated decreases in cyclic AMP accumulation in rat hippocampal slices.
abstract: N-ethylmaleimide (NEM) has been reported to interact with the GTP-binding Ni-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. Treatment of cortical membranes with NEM (100 microM for 5 min) altered the binding of [3H]-phenylisopropyladenosine (PIA) from being almost exclusively to a single class of high affinity sites (KD = 1.65 nM) to binding at two classes of sites (KDH = 2.1 nM, KDL = 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). In rat hippocampal slices treated with forskolin (0.3 microM) L-PIA produced a biphasic effect on cyclic AMP accumulation: an inhibition at 0.03 to 1 microM and at higher concentrations, a stimulation. Treatment with 50 microM NEM selectively inhibited the inhibitory phase, causing stimulation at lower concentrations of L-PIA. At 50 microM, NEM did not alter basal or forskolin-stimulated cyclic AMP accumulation but at higher concentrations inhibition was observed. It is concluded that NEM can, in certain doses, selectively block adenosine A1-receptor-mediated effects without affecting A2-receptor-mediated actions in the same tissue. It is suggested that this is due to NEM affecting the Ni guanine nucleotide binding protein.
mesh_terms: D000818:Animals; D002415:Cats; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D005033:Ethylmaleimide / Q000494:pharmacology*; D006624:Hippocampus / Q000378:metabolism*; D066298:In Vitro Techniques; D008297:Male; D008566:Membranes / Q000378:metabolism; D010660:Phenylisopropyladenosine / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000502:physiology*; D011983:Receptors, Purinergic
chemical_list: D011956:Receptors, Cell Surface; D011983:Receptors, Purinergic; D005576:Colforsin; D010660:Phenylisopropyladenosine; D000242:Cyclic AMP; D005033:Ethylmaleimide