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

ABSTRACT: Previous studies suggest that the large-conductance Ca(2+)-activated K(+) (BKCa) channel and Rho-kinase play major roles in the control of urinary bladder tone. Here, we investigated their involvement in ?-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 ?M). 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 ?-AR agonists, an effect insensitive to Y27,632. In the presence of carbachol, both ?-AR agonists increased MLC phosphorylation, an effect reduced by Y27,632 only in the presence of 1 ?M carbachol. These results indicate that the extent of BKCa channel and Rho-kinase involvement in relaxation induced by ?-AR agonists depends on pre contractile stimulus and species.

SUBMITTER: Cernecka H 

PROVIDER: S-EPMC4475246 | biostudies-literature | 2015 Jul

REPOSITORIES: biostudies-literature