Login to Access Video or Poster Abstract: MP42-14
Sources of Funding: Department of Veterans Affairs, Research Service BX001790; BX002806.

Introduction

Bladder smooth muscle (BSM) contractions in response to ATP are generally attributed to P2X1 receptor (P2X1R) activation. In rodents however, P2X1R antagonists do not completely inhibit the purinergic component of neurogenic bladder contractions, suggesting that other functionally relevant P2XR subtypes contribute to the smooth muscle response. In addition to pronounced expression of the P2X1 receptor subtype, BSM may also express P2X4R. This study examined whether the activation of P2X4R exerts a functional role in mouse and rat bladders.

Methods

P2X4R expression was investigated in BSM tissue without mucosa and cultured BSM cells from mice and rats. Longitudinal BSM strips from each species were mounted in organ bath for isometric tension studies. Purinergic contractions were elicited by α-β-methylene-ATP (αβmATP), and the purinergic component of electrical field stimulation (EFS) was isolated by pre-treatment with the muscarinic receptor antagonist atropine. Inhibitory effects of P2X4R selective antagonists, 5-BDBD or BX430, on αβmATP- and EFS-induced contractions were investigated in the presence of P2X1R antagonist NF449. The effect of ivermectin (IVC), a P2X4R positive modulator, on contractile responses to αβmATP was determined in mouse bladders.

Results

P2X4R expression was detected in BSM tissue and cultured BSM cells from both species. Though P2X1R activation is predominantly responsible for purinergic contractions in rodent bladders, a significant portion of the contractile response to both αβmATP (22.3±7%) and EFS (27.5±4% of purinergic component of EFS) was resistant to P2X1R inhibition. This P2X1R-resistant component was abolished by administration of P2X4R antagonists 5-BDBD or BX430. In addition, in mouse bladders, responses to exogenous αβmATP increased significantly (33.0±11%) in the presence of IVC.

Conclusions

Our data indicates that in rodents, a P2X4R-sensitive component of BSM contraction contributes significantly to ATP-mediated responses. Since purinergic signaling is significantly increased in overactive bladders and interstitial cystitis in humans, P2X4R may represent a potential target for the treatment of bladder dysfunction.

Funding

Department of Veterans Affairs, Research Service BX001790; BX002806.