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

Abstract

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. Bladder neck strips were mounted in organ baths containing physiological saline solution at 37°C and gassed with 95% O(2) and 5% CO(2) , for isometric force recording to endothelin receptor agonists, noradrenaline (NA), and electrical field stimulation. Endothelin ET(A) receptor expression was also determined, by both immunohistochemistry and Western blot. ET(A) receptor expression (Western blot) was observed in the muscular layer and urothelium. A strong ET(A) -immunoreactivity (ET(A) -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 ET(B) receptor agonist BQ3020 failed to promote contraction. BMS182874, an ET(A) receptor antagonist, reduced ET-1-induced contraction whereas BQ788, an ET(B) antagonist, did not change such responses. ET-1 contractions were reduced by extracellular Ca(2+) removal and by inhibition of voltage-gated Ca(2+) (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. ET(A) receptor blockade enhanced nitric oxide-dependent nerve-mediated relaxations. These results suggest that ET-1 produces contraction via muscular ET(A) receptors coupled to extracellular Ca(2+) entry via VOC (L-type) and non-VOC channels. Intracellular Ca(2+) mobilization and a Rho/Rho-kinase pathway could also be involved in these responses. ET-1-evoked potentiation on noradrenergic contraction, and neuronal ET(A) receptors modulating nitrergic inhibitory neurotransmission, are also demonstrated.