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

Abstract

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 378C 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 Ca2þ removal and by inhibition of voltage-gated Ca2þ (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 Ca2þ entry via VOC (L-type) and non-VOC channels. Intracellular Ca2þ 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.