Further studies on the motor response of the human isolated urinary bladder to tachykinins, capsaicin and electrical field stimulation.

1. Muscle strips from the dome of the human urinary bladder responded to field stimulation with contractions which were atropine- (3 microM) and tetrodotoxin- (1 microM) sensitive. These contractions were sensitive to omega conotoxin (CTX, 0.1 microM). The atropine- and tetrodotoxin-resistant contractions produced by field stimulation were totally unaffected by CTX. 2. DMPP (30-100 microM), a nicotinic agonist, produced transient bladder contractions which were hexamethonium- and atropine-sensitive. 3. Tachykinins produced a contraction of the human bladder. Among several synthetic tachykinin analogs only those having activity at the NK-2 receptor produced a consistent contractile response. 4. Either capsaicin (1 microM) or calcitonin gene-related peptide (10 nM-0.1 microM) had no motor effect. At 10 microM, capsaicin exerted a depressant effect on nerve-mediated contractions but this effect did not exhibit desensitization. 5. These findings provide evidence that NK-2 receptors are the main if not the sole mediators of the contractile response of the muscle from the dome of the human isolated bladder to tachykinins. 6. No evidence was found for a tachykininergic component in the excitatory response to field stimulation nor for motor responses mediated by capsaicin-sensitive nerves. 7. CTX-sensitive calcium channels are probably present on cholinergic nerve terminals in the human bladder muscle.