Mechanisms involved in the nitric oxide independent inhibitory neurotransmission to the pig urinary bladder neck.

Aims: The current study investigates the mechanisms involved in nitric oxide (NO)-independent, nonadrenergic, noncholinergic (NANC) inhibitory neurotransmission to the pig urinary bladder neck.

Methods: Urothelium-denuded strips were mounted in organ baths containing physiological saline solution (PSS) at 37°C for isometric force recordings. The relaxations to electrical field stimulation (EFS) were carried out on strips treated with guanethidine, atropine and N(G) -nitro-L-arginine, to block noradrenergic neurotransmission, muscarinic receptors and NO synthase, respectively, and precontracted with phenylephrine.

Results: EFS (1-16 Hz) produced frequency-dependent relaxations which were abolished by the blockade of neuronal voltage-activated Na(+) channels. Nonselective and selective inhibition of COX and COX-1, respectively, and blockade of Na(+) -K(+) ATPase reduced the EFS-induced relaxations. However, blockade of COX-2, soluble guanylyl cyclase, large-, intermediate- and small-conductance Ca(2+) -activated K(+) channels, ATP-dependent K(+) channels, voltage-gated K(+) channels, cAMPc-dependent protein kinase (PKA) and cGMP-dependent protein kinase (PKG) failed to modify the nerve-mediated relaxations.

Conclusions: The NO-independent inhibitory neurotransmission to the pig urinary bladder neck is mediated, in part, through prostanoids release from a COX-1 pathway, and through activation of the Na(+) -K(+) ATPase. PKA and PKG pathways and postjunctional K(+) channels do not appear to be involved in the NO-independent nerve-mediated relaxations.