Evidence that prejunctional adenosine receptors regulating acetylcholine release from rat hippocampal slices are linked to an N-ethylmaleimide-sensitive G-protein, but not to adenylate cyclase or dihydropyridine-sensitive Ca2+-channels.
Electrically evoked [3H]acetylcholine ([3H]ACh) release from slices of the rat hippocampus was reduced in a dose-dependent manner by the adenosine A1-receptor agonist R-phenylisopropyladenosine (R-PIA) in the concentration range 0.1-10 microM. The maximal effect was observed with 1 microM R-PIA. Treatment with N-ethylmaleimide (NEM, 100 microM, 10 min), which inactivates nucleotide-binding proteins (G-proteins), caused a slight increase in the basal overflow (0.17 +/- 0.01% v. 0.10 +/- 0.003% in the control slices), but did not affect stimulated release (0.73 +/- 0.05% vs. 0.74 +/- 0.03% in the control slices). N-ethylmaleimide pretreatment significantly reduced the prejunctional inhibitory effect of R-PIA on [3H]ACh release in a non-competitive manner. The S2/S1 ratio was 0.92 +/- 0.03 in controls and was reduced to 0.32 +/- 0.02 by 1 microM R-PIA in the control slices and to 0.57 +/- 0.03 after NEM pretreatment. Stimulation of cyclic AMP-accumulation by forskolin (1 microM) and rolipram (30 microM) before the second stimulation (S2) enhanced the S2/S1 ratio by about 30% to 1.26 +/- 0.12, but did not reduce the inhibitory effect of R-PIA (1 microM). The Ca2+-channel agonist Bay K 86(44) (1 microM), a concentration that increases K+-evoked noradrenaline release, did not affect the basal or electrically evoked [3H]ACh overflow, or the prejunctional effects of R-PIA (0.1 and 1 microM) on [3H]ACh release. Our results suggest that the presynaptic inhibitory effects of A1-receptor agonists on [3H]ACh release are exerted via a nucleotide-binding protein that can be inhibited by NEM.(ABSTRACT TRUNCATED AT 250 WORDS)
Dunér-Engström
M
M
Department of Pharmacology, Karolinska Institute, Stockholm, Sweden.
Fredholm
B B
BB
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D002121:Calcium Channel Blockers / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D004095:Dihydropyridines / Q000494:pharmacology*; D004558:Electric Stimulation; D005033:Ethylmaleimide / Q000494:pharmacology*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006624:Hippocampus / Q000378:metabolism*; D008297:Male; D010660:Phenylisopropyladenosine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011950:Receptors, Cholinergic / Q000187:drug effects / Q000502:physiology*; D017981:Receptors, Neurotransmitter / Q000187:drug effects / Q000502:physiology*; D011983:Receptors, Purinergic / Q000187:drug effects / Q000502:physiology*
D002121:Calcium Channel Blockers; D002352:Carrier Proteins; D004095:Dihydropyridines; D011950:Receptors, Cholinergic; D017981:Receptors, Neurotransmitter; D011983:Receptors, Purinergic; D010660:Phenylisopropyladenosine; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; C038806:1,4-dihydropyridine; D000242:Cyclic AMP; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D005033:Ethylmaleimide