ATP and beta,gamma-methylene ATP produce relaxation of guinea-pig isolated trachealis muscle via actions at P1 purinoceptors.

Adenosine 5'-triphosphate (ATP), beta, gamma-methylene ATP and alpha, beta-methylene ATP produced relaxation of carbachol-precontracted isolated trachealis muscle from the guinea-pig in the presence of indomethacin (2.8 microM) and the adenosine uptake inhibitor S-(4-nitrobenzyl)-6-thioinosine (NBTI; 300 nM). The potency order for ATP and analogues was: beta, gamma-methylene ATP = ATP > alpha, beta-methylene ATP = uridine 5'-triphosphate (UTP) = 2-methylthio ATP. Adenosine and 5'-N-ethylcarboxamidoadenosine (NECA) also caused relaxation. Relaxations to ATP, beta, gamma-methylene ATP, adenosine and NECA were not inhibited by the P2 purinoceptor antagonist suramin (100 microM), but were inhibited by the P1 purinoceptor antagonist 8-sulphophenyltheophylline (140 microM). NBTI significantly potentiated adenosine and ATP but not beta, gamma-methylene ATP or NECA. The data are compatible with the idea that beta, gamma-methylene ATP could interact directly with P1 purinoceptors while ATP acts indirectly at P1 purinoceptors via conversion to adenosine.