Subtypes of purinoceptors in rat and dog urinary bladder smooth muscles

1. Both adenosine and adenosine 5'-triphosphate (ATP) (10 microM and 100 microM) relaxed 10 microM acetylcholine (ACh)-induced contraction of rat bladder strips, which was completely antagonized by 100 microM 8-(p-sulphophenyl) theophylline. In dog bladder neither adenosine nor ATP inhibited ACh-induced contraction. 2. P2x-purinoceptor agonists contracted both rat and dog bladder strips with the potency order of alpha,beta-MeATP > ATP > ADP. 3. Alpha,beta-MeADP (100 microM) induced a contraction of the rat bladder strip even after desensitization of P2x-purinoceptors but failed to contract the dog bladder strip. 4. 2-MeSATP (1 microM to 300 microM) concentration-dependently induced contraction of rat bladder strips; this contraction was significantly inhibited after desensitization of P2x-purinoceptors. Cibacron blue 3GA (100 microM) antagonized the drug at concentrations lower than 30 microM, whereas it augmented the response to the drug at concentrations above 30 microM. 5. ADP beta S (1 microM to 1 mM) concentration-dependently induced contraction of rat bladder strips after desensitization of P2x-purinoceptors; a contraction which was significantly antagonized by cibacron blue 3GA (100 microM). 6. It is concluded that three subtypes of purinoceptors, P1 (mediating relaxation), and P2x and another type of P2 (mediating contraction), exist in rat urinary bladder smooth muscle, whereas a single subtype of the receptor, P2x-purinoceptor (mediating contraction) occurs in dog urinary bladder smooth muscle.