Effects of N-ethylmaleimide and forskolin on glutamate release from rat hippocampal slices. Evidence that prejunctional adenosine receptors are linked toN-proteins, but not to adenylate cyclase

Abstract

In the present experiments we have examined the effect of N-ethylmaleimide (NEM) on the release of [³H] glutamate from rat hippocampal slices. Pretreatment of slices with NEM in a concentration between 50 μM and 200 μM, can inhibit the GTP-binding protein (N) that transmitts receptor signals into inhibitions of adenylate cyclase, without affecting the N_s-protein, that transmits signals into stimulation of the cyclase, or the cyclase. The adenosine receptor agonist R-phenylisopropyladenosine (R-PIA, I μM) caused an approximately 50% inhibition of the evoked [³H] glutamate release. This effect was completely prevented by NEM treatment, which did not affect basal or stimulated release of the amino acid. By contrast, the effect of R-PIA was unaffected by adding an adenylate cyclase stimulator (forskolin 1 μM) and a phosphodiesterase inhibitor (rolipram, ZK 62.711, 30 μM) which raised the cyclic AMP content of the slices approximately 1 o-fold. In conclusion, these results suggest that the adenosine receptor that mediates prejunctional inhibition of glutamate release is coupled to a protein similar to the N₁-protein, but that another effector than adenylate cylase is involved.,