β3-Adrenoceptor-mediated relaxation of rat and human urinary bladder: roles of BKCa channels and Rho kinase.

Hana Cernecka,Martin C Michel,Igle Jan De Jong,Kim Kersten,Carolina R Elzinga,Cees Korstanje,Martina Schmidt,Harm Maarsingh

doi:10.1007/s00210-015-1128-z

Abstract

Previous studies suggest that the large-conductance Ca2+-activated K+ (BKCa) channel and Rho-kinase play major roles in the control of urinary bladder tone. Here, we investigated their involvement in β-adrenoceptor (AR)-mediated relaxation of rat and human bladder. Concentration-response curves of isoprenaline and mirabegron-induced bladder relaxation were generated against passive tension and KCl- and carbachol-induced tone, in the absence or presence of the BKCa channel inhibitor iberiotoxin (100 nM) or the Rho-kinase inhibitor Y27,632 (1 μM). Myosin light chain (MLC) phosphorylation was studied by Western blot. In rat, iberiotoxin only slightly altered isoprenaline- and mirabegron-induced relaxation against KCl-induced tone but attenuated relaxation by both agonists against carbachol-induced tone. Y27,632 enhanced isoprenaline- or mirabegron-induced relaxation only against carbachol-induced tone. In humans, iberiotoxin slightly enhanced relaxation by both agonists against carbachol-induced pre-contraction. Y27,632 did not change isoprenaline-induced relaxation but enhanced that by mirabegron. Under passive tension, MLC phosphorylation was markedly reduced by both β-AR agonists, an effect insensitive to Y27,632. In the presence of carbachol, both β-AR agonists increased MLC phosphorylation, an effect reduced by Y27,632 only in the presence of 1 μM carbachol. These results indicate that the extent of BKCa channel and Rho-kinase involvement in relaxation induced by β-AR agonists depends on pre contractile stimulus and species.Electronic supplementary materialThe online version of this article (doi:10.1007/s00210-015-1128-z) contains supplementary material, which is available to authorized users.

Highlights

Introduction βAdrenoceptors (ARs) mediate urinary bladder relaxation (Michel and Vrydag 2006) and have shown efficacy in experimental models of detrusor overactivity (Michel and Barendrecht 2008)
The canonical signalling pathway of β-ARs is stimulation of adenylyl cyclase to form cyclic adenosine monophosphate. This results in activation of protein kinase A (PKA) which can suppress calcium-calmodulin-dependent myosin/ actin interaction upon phosphorylation of myosin light chain kinase
The degree of passive tension (5, 10 and 15 mN) in human bladder strips had no major effect on the relaxation responses to isoprenaline or mirabegron

Summary

Introduction

Introduction βAdrenoceptors (ARs) mediate urinary bladder relaxation (Michel and Vrydag 2006) and have shown efficacy in experimental models of detrusor overactivity (Michel and Barendrecht 2008). The canonical signalling pathway of β-ARs is stimulation of adenylyl cyclase to form cyclic adenosine monophosphate (cAMP) This results in activation of protein kinase A (PKA) which can suppress calcium-calmodulin-dependent myosin/ actin interaction upon phosphorylation of myosin light chain kinase. While this could plausibly contribute to detrusor smooth muscle relaxation (Andersson and Arner 2004; Hashitani et al 2004), studies with adenylyl cyclase or PKA inhibitors have detected only a small, if any, role for this pathway in bladder relaxation (Frazier et al 2008). The identity and functional collaboration of these pathways is poorly understood; with regard to human bladder relaxation, even the roles of cAMP/PKA and BKCa have only been poorly characterized

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