Treatment with N‐ethylmaleimide selectively reduces adenosine receptor‐mediated decreases in cyclic AMP accumulation in rat hippocampal slices

Abstract

1 N-ethylmaleimide (NEM) has been reported to interact with the GTP-binding N1-protein; we have examined its effect on adenosine receptor binding in feline cortical membranes and on adenosinereceptor mediated effects on cyclic AMP accumulation in rat hippocampal slices.

The adenosine receptor‐mediated inhibition of noradrenaline release possibly involves a N‐protein and is increased by α2‐autoreceptor blockade

“…Analogous effects of NEM on agonist and antagonist binding and inhibition of adenylate cyclase were obtained in rat hippocampal slices (Yeung & Green, 1983;Fredholm et al, 1985). Fredholm & Lindgren (1986) In the presence of the ac2-adrenoceptor antagonist yohimbine, which increased noradrenaline release by autoreceptor blockade, the inhibitory action of (-)-PIA was markedly enhanced.…”

“…These observations are similar to those obtained with the SH-reagent N-ethylmaleimide (NEM). NEM attenuated or abolished the a-adrenoceptor (Jakobs et al, 1982), the muscarinic receptor (Harden et al, 1982) and the adenosine receptormediated (Ukena et al, 1984;Fredholm et al, 1985) inhibition of adenylate cyclase and mimicked the effect of guanine nucleotides on agonist binding to these receptors (Harden et al, 1982;Yeung & Green, 1983;Quennedy et al, 1984;Ukena et al, 1984;Fredholm et al, 1985).…”

Solubilization of A1 adenosine receptor from pig brain: Characterization and evidence of the role of the cell membrane on the coexistence of high‐ and low‐affinity states

“…One measure of this interaction that is demonstrable in vitro is the regulation of receptor binding by guanine nucleotides and bivalent cations Green, 1983, 1984;Lohse et al, 1984). Guanine nucleotides or analogues such as Gpp(NH)p cause transition of the high-affinity to the low-affinity state (Lohsc et a]., 1984;Fredholm et al. 1985;Frame et al, 1986;Rarnkumar and Stiles, 1988), whereas bivalent cations selectively increase the overall affinity of agonists for the A, receptor (Klotz et al, 1986;Perez-Reyes et al, 1986;Yeung et a]., 1987).…”

Further Elucidation of a Pertussis Toxin-Sensitive Transmembrane Signaling Mechanism Involved in Central α(2)-Adrenoceptor Activation in the Rat

“…In this regard, the concentration of Nethylmaleimide (800 gA/) we employed for microinjection into the bilateral NRGC was higher than the 50-200 gM used to inhibit Gi [10], Likewise, phorbol 12-myristate 13-acetate (800 pM) was greater than 200 nM required to cause a feedback inhibition on inositol phospholipid metabolism [29]. Similarly, our concentrations of cholera toxin (120 ilM) and forskolin (12 mM) were sufficient to prolong Gs [13] or activate adenylyl cyclase [24], Pertussis toxin causes an increase in the Kd value of [3H]-clonidine (an a2-adrenoceptor agonist similar to gua nabenz) binding in cortical membrane of rat brain [22], and a reduction in the affinity of epinephrine for [3H]-yohimbine (a specific a2-adrenoceptor antagonist) binding sites in renal tissues [4], Such altered binding characteris tics of the a2-adrenoceptors may conceivably be reflected by the reduced circulatory depressive efficacy of guana benz, as observed in the present study.…”

“…N-ethylmaleimide, which at a low concentration (mi cromolar range) inhibits Gi by uncoupling its a-subunit from GTP [10,17], did not significantly antagonize the cardiovas cular effects of guanabenz. It should be mentioned that, by inhibiting adenylyl cyclase activity [18,22], Gi has generally been associated with the modulation of norepinephrine release by presynaptic a2-adrenoceptors [1,2,10]. On the other hand, we previously reported [8] that the cardiovascular suppressant effect of guanabenz engages primarily the postsynaptic a2-adrenoceptors in the NRGC.…”