Effects of allopurinol, erythro-9-(2-hydroxy-3-nonyl)adenine and S-(4-nitrobenzyl)-6-thioinosine on the degradation of adenosine 5′-triphosphate in the rat colon muscularis mucosae

1 The effects on ATP breakdown of some modulators of adenosine transport or metabolism were studied in the rat colon muscularis mucosae, a tissue which contracts to ATP and is thought to contain P2Y₁ receptors. The compounds tested were the xanthine oxidase inhibitor allopurinol, the adenosine deaminase inhibitor erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA) and the adenosine uptake blocker S-(4-nitrobenzyl)-6-thioinosine (NBTI).

2 The degradation of adenosine 5′-triphosphate (ATP) (100 μm) and the appearance of metabolites was followed by high pressure liquid chromatography during incubation of isolated tissue preparations alone or in the presence of the drugs, following preincubation with the drugs for 1 h.

3 In the absence of drugs ATP was rapidly degraded by the rat colon muscularis mucosae with a half-life of 6.1 ± 0.7 min, the major breakdown product being inosine rather than adenosine. Allopurinol (1 μm) and NBTI (10 μm) had no effect on the rate of breakdown of ATP or on the pattern of metabolites produced. EHNA (1 or 10 μm) also had no effect on the half-life of ATP, but in the presence of EHNA (1 μm) the rate of production of inosine was significantly reduced and some adenosine was detected, while in the presence of 10 μm EHNA the production of inosine was abolished and adenosine became the final breakdown product.

4 These results indicate that allopurinol (1 μm) and NBTI (10 μm) have no detectable effect on extracellular purine metabolism in this tissue, and that the build-up of adenosine produced by treatment with EHNA does not have a feedback effect on ATP breakdown.