Role of P2X(4) Receptor in Mouse Voiding Function

Purinergic signalling plays an important role in the regulation of bladder smooth muscle (BSM) contractility, and P2X(4) receptor is expressed in the bladder wall, where it may act by forming heteromeric receptors with P2X(1), the major purinergic force-generating muscle receptor. To test this hypothesis, we examined mouse BSM contractile properties in the absence and presence of selective P2X(1) (NF449 & NF279) and P2X(4) antagonists (5-BDBD). These drugs inhibited BSM purinergic contraction only partially, suggesting the possibility of a heteromeric receptor. However, carefully controlled co-immunoprecipitation experiments indicated that P2X(1) and P2X(4) do not form physically linked heteromers. Furthermore, immunofluorescence staining showed that P2X(4) is not present in mouse BSM per se, but in an unknown cellular structure among BSM bundles. To investigate whether deletion of P2X(4) could impact voiding function in vivo, P2X(4) null mice were characterized. P2X(4) null mice had normal bladder weight and morphology, normal voiding spot size and number by voiding spot assay, normal voiding interval, pressure and compliance by cystometrogram, and normal BSM contractility by myography. In conclusion, these data strongly suggest that P2X(4) is not present in mouse BSM cells, does not affect smooth muscle contractility and that mice null for P2X(4) exhibit normal voiding function.