The P2Y2 receptor sensitizes mouse bladder sensory neurons and facilitates purinergic currents

Sensitization of bladder afferents is an underlying contributor to the development and maintenance of painful bladder syndrome/interstitial cystitis. Extracellular purines and pyrimidines (e.g., ATP and UTP), released during bladder distension or from damaged cells after tissue insult, are thought to play an important role in bladder physiological and pathological states by actions at ionotropic P2X and metabotropic P2Y receptors. In the present study, we examined the ability of P2Y receptors to sensitize and modulate P2X-mediated responses in mouse bladder sensory neurons. UTP (a P2Y(2) and P2Y(4) agonist) increased excitability of bladder neurons by depolarizing resting membrane potential, increasing action potential firing, and facilitating responses to suprathreshold current injection as well as to P2X agonist application. These effects of UTP on bladder neuron excitability were blocked by the P2Y(2) receptor antagonist suramin. UTP also facilitated bladder neuron homomeric P2X(2) sustained currents and homomeric P2X(3) fast currents. The facilitatory effect of UTP on P2X(2) sustained currents was mediated by a G-protein-coupled P2Y(2) receptor/PKC pathway, whereas the effect of UTP on P2X(3) fast currents was G-protein independent. We also examined P2X and P2Y receptor expression in bladder neurons. P2Y(2) and P2Y(4) transcripts were detected in approximately 50 and approximately 20% of bladder neurons, respectively. Approximately 50% of P2X(2)- and P2X(3)-positive bladder neurons expressed P2Y(2) transcripts, whereas < or =25% of the same bladder neurons expressed P2Y(4) transcripts. These results support involvement of P2Y(2) receptors in bladder sensation, suggesting an important contribution to bladder neuron excitability and hypersensitivity.