Negative crosstalk between M1 and M2 muscarinic autoreceptors involves endogenous adenosine activating A1 receptors at the rat motor endplate.
At the rat motor nerve terminals, activation of muscarinic M(1) receptors negatively modulates the activity of inhibitory muscarinic M(2) receptors. The present work was designed to investigate if the negative crosstalk between muscarinic M(1) and M(2) autoreceptors involved endogenous adenosine tonically activating A(1) receptors on phrenic motor nerve terminals. The experiments were performed on rat phrenic nerve-hemidiaphragm preparations loaded with [(3)H]-choline (2.5 microCi/ml). Selective activation of muscarinic M(1) and adenosine A(1) receptors with 4-(N-[3-clorophenyl]-carbamoyloxy)-2-butyryltrimethylammonium (McN-A-343, 3 microM) and R-N(6)-phenylisopropyladenosine (R-PIA, 100 nM), respectively, significantly attenuated inhibition of evoked [(3)H]-ACh release induced by muscarinic M(2) receptor activation with oxotremorine (10 microM). Attenuation of the inhibitory effect of oxotremorine (10 microM) by R-PIA (100 nM) was detected even in the presence of pirenzepine (1 nM) blocking M(1) autoreceptors, suggesting that suppression of M(2)-inhibiton by A(1) receptor activation is independent on muscarinic M(1) receptor activity. Conversely, the negative crosstalk between M(1) and M(2) autoreceptors seems to involve endogenous adenosine tonically activating A(1) receptors. This was suggested, since attenuation of the inhibitory effect of oxotremorine (10 microM) by McN-A-343 (3 microM) was suppressed by the A(1) receptor antagonist, 1,3-dipropyl-8-cyclopentylxanthine (2.5 nM), and by reducing extracellular adenosine with adenosine deaminase (0.5 U/mL) or with the adenosine transport blocker, S-(p-nitrobenzyl)-6-thioinosine (NBTI, 10 microM). The results suggest that the negative crosstalk between muscarinic M(1) and M(2) autoreceptors involves endogenous adenosine outflow via NBTI-sensitive (es) nucleoside transport system channelling to the activation of presynaptic inhibitory A(1) receptors at the rat motor endplate.
Laboratório de Farmacologia e Neurobiologia, Unidade Multidisciplinar de Investigação Biomédica (UMIB), Instituto de Ciências Biomédicas de Abel Salazar (ICBAS) - Universidade do Porto, L. Prof. Abel Salazar, 2, 4099-003 Porto, Portugal.
Laura
L
Oliveira
Maria Alexandrina
MA
Timóteo
Paulo
P
Correia-de-Sá
D008455:(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethylammonium Chloride / Q000008:administration & dosage; D000109:Acetylcholine / Q000378:metabolism; D000241:Adenosine / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000378:metabolism; D058907:Adenosine A1 Receptor Agonists; D000243:Adenosine Deaminase / Q000378:metabolism; D000818:Animals; D005260:Female; D008297:Male; D009045:Motor Endplate / Q000187:drug effects / Q000378:metabolism*; D018377:Neurotransmitter Agents / Q000008:administration & dosage; D033703:Nucleoside Transport Proteins / Q000037:antagonists & inhibitors; D010095:Oxotremorine / Q000008:administration & dosage; D010791:Phrenic Nerve / Q000187:drug effects / Q000378:metabolism; D010890:Pirenzepine / Q000008:administration & dosage; D051381:Rats; D017208:Rats, Wistar; D043682:Receptor, Adenosine A1 / Q000378:metabolism*; D043643:Receptor, Muscarinic M1 / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*; D043585:Receptor, Muscarinic M2 / Q000819:agonists / Q000378:metabolism*; D013868:Thioinosine / Q000008:administration & dosage / Q000031:analogs & derivatives; D014316:Tritium; D014970:Xanthines / Q000008:administration & dosage
D058907:Adenosine A1 Receptor Agonists; D018377:Neurotransmitter Agents; D033703:Nucleoside Transport Proteins; D043682:Receptor, Adenosine A1; D043643:Receptor, Muscarinic M1; D043585:Receptor, Muscarinic M2; D014970:Xanthines; C444719:adenosine transporter; D014316:Tritium; C047235:N-(1-methyl-2-phenylethyl)adenosine; D010890:Pirenzepine; D013868:Thioinosine; D008455:(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethylammonium Chloride; D010095:Oxotremorine; C051360:1,3-dipropyl-8-cyclopentylxanthine; D000243:Adenosine Deaminase; C001789:4-nitrobenzylthioinosine; D000241:Adenosine; D000109:Acetylcholine