Neuronal and non-neuronal bradykinin receptors are involved in the contraction and/or relaxation to the pig bladder neck smooth muscle
Abstract
Aims
The current study investigates the role played by bradykinin (BK) receptors in the contractility to the pig bladder neck smooth muscle.
Methods
Bladder neck strips were mounted in myographs for isometric force recordings and BK receptors expression was also determined by immunohistochemistry.
Results
B2 receptor expression was observed in the muscular layer and urothelium whereas B1 expression was consistent detected in urothelium. A strong B2 immunoreactivity was also observed within nerve fibers among smooth muscle bundles. On urothelium-denuded preparations basal tone, BK induced concentration-dependent contractions which were reduced in urothelium-intact samples, by extracellular Ca2+ removal and by blockade of B2 receptors and voltage-gated Ca2+ (VOC) and non-VOC channels, and increased by cyclooxygenase (COX) inhibition. On phenylephrine-precontracted denuded strips, under non-adrenergic non-cholinergic (NANC) conditions, electrical field stimulation-elicited frequency-dependent relaxations which were reduced by B2 receptor blockade. In urothelium-intact samples, the B1 receptor agonist kallidin promoted concentration-dependent relaxations which were reduced by blockade of B1 receptors, COX, COX-1 and large-conductance Ca2+-activated K+ (BKCa) channels and abolished in urothelium-denuded samples and in K+-enriched physiological saline solution-precontracted strips.
Conclusions
These results suggest that BK produces contraction of pig bladder neck via smooth muscle B2 receptors coupled to extracellular Ca2+ entry via VOC and non-VOC channels with a minor role for intracellular Ca2+ mobilization. Facilitatory neuronal B2 receptors modulating NANC inhibitory neurotransmission and urothelial B1 receptors producing relaxation via the COX-1 pathway and BKCa channel opening are also demonstrated. Neurourol. Urodynam. 33:558–565, 2014. © 2013 Wiley Periodicals, Inc.
