A1 and A2A receptor activation by endogenous adenosine is required for VIP enhancement of K+ -evoked [3H]-GABA release from rat hippocampal nerve terminals.
Vasoactive intestinal peptide (VIP) modulates GABA release from hippocampal nerve terminals and enhances hippocampal synaptic transmission through a pathway dependent on GABAergic transmission. Since VIP modulation of hippocampal synaptic transmission is dependent on the tonic actions of adenosine we investigated if endogenous adenosine could influence VIP enhancement of GABA release from isolated hippocampal nerve endings, and which adenosine receptors could be mediating this influence. When extracellular endogenous adenosine was removed using adenosine deaminase (ADA, 1U/ml), the enhancement (57.2+/-3.7%) caused by VIP on GABA release was prevented. Blockade of adenosine A(1) receptors with 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, 10nM) or of A(2A) receptors with ZM241385 (50nM) abolished the effect of VIP. In the presence of ADA, selective A(2A) receptor-activation with CGS21680 (10nM) readmitted most of the enhancement caused by VIP on GABA release (50.7+/-5.3%). Also in the presence of ADA, A(1) receptor activation with N(6)-cyclopentyladenosine (CPA, 50nM) partially readmitted that effect of VIP (32.6+/-3.8%). In conclusion, the enhancement of GABA release caused by VIP in hippocampal nerve terminals is dependent on the tonic actions of adenosine on both A(1) and A(2A) receptors, and this action of adenosine is essential to VIP modulation of GABA release.
Institute of Pharmacology and Neurosciences, Faculty of Medicine and Institute of Molecular Medicine, University of Lisbon, Avenida Prof. Egas Moniz, 1649-028 Lisbon, Portugal. diana-reis@fm.ul.pt
Diana
D
Cunha-Reis
Joaquim A
JA
Ribeiro
Ana M
AM
Sebastião
D000241:Adenosine / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D000243:Adenosine Deaminase / Q000494:pharmacology; D000818:Animals; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D010627:Phenethylamines / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D043682:Receptor, Adenosine A1 / Q000187:drug effects / Q000378:metabolism; D043705:Receptor, Adenosine A2A / Q000187:drug effects / Q000378:metabolism; D018047:Receptors, Purinergic P1 / Q000187:drug effects / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism; D014316:Tritium; D014660:Vasoactive Intestinal Peptide / Q000378:metabolism* / Q000494:pharmacology; D014970:Xanthines / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D010627:Phenethylamines; D043682:Receptor, Adenosine A1; D043705:Receptor, Adenosine A2A; D018047:Receptors, Purinergic P1; D014970:Xanthines; D014316:Tritium; C061282:2-(4-(2-carboxyethyl)phenethylamino)-5'-N-ethylcarboxamidoadenosine; D014660:Vasoactive Intestinal Peptide; C048599:N(6)-cyclopentyladenosine; D005680:gamma-Aminobutyric Acid; C051360:1,3-dipropyl-8-cyclopentylxanthine; D000243:Adenosine Deaminase; D000241:Adenosine; D011188:Potassium