title: Effects of N-ethylmaleimide and forskolin on noradrenaline release from rat hippocampal slices. Evidence that prejunctional adenosine and alpha-receptors are linked to N-proteins but not to adenylate cyclase.
abstract: N-ethylmaleimide (NEM) treatment has been shown to inactivate regulatory GTP-binding N (G)-proteins in many preparations, including slices of rat hippocampus. NEM-treatment (100 microM for 15 min) has been used to examine the possible involvement of a N-protein in the prejunctional inhibitory effect of an adenosine analogue, R-PIA acting on A1-receptors, and of clonidine acting on alpha 2-adrenoceptors in this tissue. NEM treatment significantly enhanced basal overflow of [3H]NA and the overflow stimulated by low (0.3 Hz) frequency stimulation, but not the overflow stimulated by higher (1-10 Hz) frequency stimulation. The prejunctional inhibitory effect of R-PIA (1 microM) on NA release, stimulated by a 3 Hz stimulation, was abolished by NEM pretreatment, which also eliminated the dose-dependent prejunctional effect of clonidine and reduced the facilitatory effect of yohimbine. Forskolin had a small, but significant stimulatory effect on NA overflow, but did not reduce the prejunctional inhibitory effect of R-PIA. The adenylate cyclase inhibitor SQ 22, 536 did not reduce NA overflow. These results show that NEM blocks a critical step in the prejunctional action of both adenosine- and alpha 2-receptor agonists, which may be a N-protein. The possibility is discussed that the prejunctional A1- and alpha 2-receptors couple to a N-protein that controls a different effector than adenylate cyclase.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D005576:Colforsin / Q000494:pharmacology*; D000242:Cyclic AMP / Q000378:metabolism; D005033:Ethylmaleimide / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006624:Hippocampus / Q000378:metabolism*; D008297:Male; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009469:Neuromuscular Junction / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects*; D011983:Receptors, Purinergic / Q000187:drug effects*; D009435:Synaptic Transmission / Q000187:drug effects
chemical_list: D009419:Nerve Tissue Proteins; D011942:Receptors, Adrenergic, alpha; D011983:Receptors, Purinergic; D005576:Colforsin; D000242:Cyclic AMP; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D005033:Ethylmaleimide; D009638:Norepinephrine