Sensitization of pelvic afferent nerves in the in vitro rat urinary bladder-pelvic nerve preparation by purinergic agonists and cyclophosphamide pretreatment.

Effects of purinergic agonists (alpha,beta-meATP and ATP) and cyclophosphamide-induced cystitis on bladder afferent nerve (BAN) activity were studied in an in vitro bladder-pelvic nerve preparation. Distension of the bladder induced spontaneous bladder contractions that were accompanied by multiunit afferent firing. Intravesical administration of 40 and 130 microM alpha,beta-meATP increased afferent firing from 27 +/- 3 to 53 +/- 6 and 61 +/- 2 spikes/s, respectively, but did not change the maximum amplitude of spontaneous bladder contractions. Electrical stimulation on the surface of the bladder elicited action potentials (AP) in BAN. alpha,beta-meATP decreased the voltage threshold from 9.0 +/- 1.2 to 3.5 +/- 0.5 V (0.15-ms pulse duration) and increased the area of the APs (82% at 80-V stimulus intensity). These effects were blocked by TNP-ATP (30 microM). ATP (2 mM) applied in the bath produced similar changes in BAN activity. These effects were blocked by bath application of PPADS (30 microM). Neither TNP-ATP nor PPADS affected BAN activity induced by distension of the bladder. Cystitis induced by pretreatment of the rats with cyclophosphamide (100 mg/kg ip) increased afferent firing in response to isotonic bladder distension (10-40 cmH(2)O), decreased the threshold, and increased the area of evoked APs. The increase in afferent firing at 10 cmH(2)O intravesical pressure was reduced 52% by PPADS. These results indicate that purinergic agonists acting on P2X receptors and cystitis induced by cyclophosphamide can increase excitability of the BANs.