EVIDENCE OF ADENOSINE 5′-TRIPHOSPHATE RELEASE FROM NERVE AND P2X-PURINOCEPTOR MEDIATED CONTRACTION DURING ELECTRICAL STIMULATION OF RAT URINARY BLADDER SMOOTH MUSCLE

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Abstract
Purpose: We provided direct evidence for the existence of purinergic innervation in the rat urinary bladder. Materials and Methods: The non-adrenergic non-cholinergic (NANC) innervation was studied in 4-month-old Wistar rats. Electric-field stimulation (EFS) of the detrusor muscle strips in the presence of four autonomic blockers (atropine 10 sup −6 M, guanethidine 10 sup −6 M, phentolamine 10 sup −6 M and propranolol 10 sup −6 M) showed NANC contractions accounted for about 50% of the maximum contractile response. The adenyl purines released from nerves by EFS were detected by HPLC after conversion to ethenopurines. The amount of total purine released was frequency-dependent and could be totally suppressed by tetradotoxin (10 sup −6 M). The amount of ATP released was significantly greater than those for ADP, AMP and adenosine (p <0.05, n = 4). Desensitization induced by alpha, beta-MeATP (10 sup −6 to 10 sup −4 M), a P2x receptor agonist, reduced the NANC contraction. In addition, the NANC contraction was also abolished by P2 receptor blocker suramin (10 sup −4 to 10 sup −3 M) and P2x receptor blocker PPADS (10 sup −5 to 10 sup −4 M.). Conclusion: The results of the present study give evidence to support purinergic nerve-mediated bladder smooth muscle contractions in the rat. Among the purine nucleotides, ATP is the dominant purinergic neurotransmitter released and P2x receptor activation is responsible for the NANC contractile response.