Mechanisms involved in endothelin-1-induced contraction of the pig urinary bladder neck

Aims There is no information about the signaling pathways involved in the endothelin-1 (ET-1)-induced contraction of bladder neck. The current study investigates the mechanisms involved in the ET-1-elicited contraction in the pig bladder neck. Methods Bladder neck strips were mounted in organ baths containing physiological saline solution at 37°C and gassed with 95% O2 and 5% CO2, for isometric force recording to endothelin receptor agonists, noradrenaline (NA), and electrical field stimulation. Endothelin ETA receptor expression was also determined, by both immunohistochemistry and Western blot. Results ETA receptor expression (Western blot) was observed in the muscular layer and urothelium. A strong ETA-immunoreactivity (ETA-IR) was identified within nerve fibers among smooth muscle bundles. ET-1 and ET-2 evoked similar concentration-dependent contractions of urothelium-denuded preparations. ET-3 produced a slight response, whereas the ETB receptor agonist BQ3020 failed to promote contraction. BMS182874, an ETA receptor antagonist, reduced ET-1-induced contraction whereas BQ788, an ETB antagonist, did not change such responses. ET-1 contractions were reduced by extracellular Ca2+ removal and by inhibition of voltage-gated Ca2+ (VOC) (L-type) and non-VOC channels, Rho/Rho-kinase pathway, and neuronal VOC channels. NA produced contractions which were enhanced by ET-1 threshold concentrations. ETA receptor blockade enhanced nitric oxide-dependent nerve-mediated relaxations. Conclusions These results suggest that ET-1 produces contraction via muscular ETA receptors coupled to extracellular Ca2+ entry via VOC (L-type) and non-VOC channels. Intracellular Ca2+ mobilization and a Rho/Rho-kinase pathway could also be involved in these responses. ET-1-evoked potentiation on noradrenergic contraction, and neuronal ETA receptors modulating nitrergic inhibitory neurotransmission, are also demonstrated. Neurourol. Urodynam. 31:156–161, 2012. © 2011 Wiley Periodicals, Inc.