Development of fast purinergic transmission in the mouse vas deferens

ATP released by sympathetic varicosities of the mouse vas deferens binds to P2X receptors which activate fast, ligand-gated channels, resulting in depolarisation of smooth muscle cells. We examined the development of fast neuromuscular transmission at surface longitudinal smooth muscle fibres of the mouse vas deferens. Sympathetic varicosities were visualised using DiOC(2)(5)-fluorescence to aid in positioning loose patch electrodes over small sets of sympathetic varicosities to record the nerve terminal impulse (NTI) and excitatory junction currents (EJCs) evoked during nerve stimulation. At the earliest age at which EJCs could be detected, 21 days postnatal (PN), most recording sites rarely showed a detectable EJC over 100 trials, even though NTIs were recorded without failure. The extent of such intermittence in transmitter release progressively declined between 21 and 42 days PN. In addition, the mean amplitude of spontaneous EJCs (SEJCs) and EJCs increased by 2- and 2.4-fold, respectively, between 21 and 42 days PN. The rise time of EJCs varied widely at each age but declined with development (e.g., 7-14 ms at 28 days PN, 3-12 ms at 42 days PN). All EJCs were abolished by suramin (100 microM). Fast rise time EJCs were rapidly abolished by alpha,beta-methylene ATP (20 microM) while some (34%) of the slower rise time EJCs were resistant to rapid desensitisation of this kind. P2X(1) and P2X(2) mRNAs were detected by reverse transcription and polymerase chain reaction (RT-PCR) to determine whether levels of expression of the receptor subunits might explain the increased EJC amplitude. Between 10 and 42 days PN no marked change was observed in the P2X(2) receptor mRNA or beta-actin mRNA (control). In contrast, the intensity of the RT-PCR band for P2X(1) receptor showed a progressive approximately 4.3-fold developmental increase relative to the P2X(2) band. These observations suggest that both prejunctional and postjunctional mechanisms cause the maturation of fast purinergic junctional transmission at the longitudinal muscle of the mouse vas deferens between 21 and 42 days PN.