Signalling to contractile proteins by muscarinic and purinergic pathways in neurally stimulated bladder smooth muscle

Abstract

Key points• Parasympathetic nerves release the neurotransmitters ATP and acetylcholine that activate purinergic and muscarinic receptors, respectively, to initiate contraction of urinary bladder smooth muscle.• Although both receptors mediate Ca 2+ influx for myosin regulatory light chain (RLC) phosphorylation necessary for contraction, the muscarinic receptor may also recruit cellular mechanisms affecting the Ca 2+ sensitivity of RLC phosphorylation.• Using transgenic mice expressing Ca 2+ /calmodulin sensor myosin light chain kinase (MLCK) in smooth muscles, the effects of selective purinergic or muscarinic receptor inhibition were examined on neurally stimulated tissues in relation to signalling pathways converging on RLC phosphorylation.• Purinergic-mediated Ca 2+ signals provide the initial Ca 2+ /calmodulin activation of MLCK with muscarinic receptors supporting sustained responses.• Activation of muscarinic receptors leads phosphorylation of myosin light chain phosphatase inhibitor CPR-17 to enhance Ca 2+ sensitivity while also initiating phosphorylation-dependent Ca 2+ desensitization of MLCK. The interplay between Ca 2+ sensitization and desensitization mechanisms fine tunes the contractile signalling module for force development.Abstract Urinary bladder smooth muscle contraction is triggered by parasympathetic nerves, which release ATP and acetylcholine (ACh) that bind to purinergic and muscarinic receptors, respectively. Neuronal signalling may thus elicit myosin regulatory light chain (RLC) phosphorylation and contraction through the combined, but distinct contributions of these receptors. Both receptors mediate Ca 2+ influx whereas muscarinic receptors may also recruit Ca 2+ -sensitization mechanisms. Using transgenic mice expressing calmodulin sensor myosin light chain kinase (MLCK) in smooth muscles, the effects of suramin/α,β-methyleneATP (α,β-meATP) (purinergic inhibition) or atropine (muscarinic inhibition) on neurally stimulated elevation of [

BK Channel-Mediated Relaxation of Urinary Bladder Smooth Muscle: A Novel Paradigm for Phosphodiesterase Type 4 Regulation of Bladder Function

“…Meanwhile, activation of G q -coupled M 3 Rs evokes Ca 21 release via inositol trisphosphate receptors, increases protein kinase C activity, inhibits TBKCs, and depolarizes DSM cell MP . As a consequence, activation of MRs, particularly M 3 R activation, increases Ca 21 influx, elevates intracellular Ca 21 levels, and enhances DSM contractility (Shahab et al, 2012;Tsai et al, 2012;Parajuli and Petkov, 2013;Yu et al, 2013). The current study indicates that the selective inhibition of PDE4 counteracts the activation of MRs and suppresses carbachol-and EFS-induced DSM contractions (Figs.…”

“…In contrast to the inhibition of PDE4, the activation of MRs by carbachol, a chemically stable MR agonist, or ACh released from parasympathetic nerves increases DSM phasic contractions (Hashitani et al, 2004;Tsai et al, 2012). Specifically, activation of G i -coupled M 2 Rs leads to an inhibition of adenylyl cyclases and a reduction in cAMP production and PKA activity (Shahab et al, 2012).…”

Effect of type II diabetes on male rat bladder contractility

“…This is consistent with our differential responses to the exogenous addition of agonist and EFS, although we did not examine a potential role of ICC. Differential signaling in response to activation of muscarinic and purinergic receptors was shown by Tsai et al (45) during EFS-induced contractions. They demonstrated that the initial phase of a murine bladder smooth muscle contraction was more dependent on purinergic receptor-mediated activation of the myosin light chain (MLC) kinase and MLC phosphorylation whereas the sustained contraction relies more on muscarinic receptor activation and phosphorylation of the Ca 2ϩ -sensitizing protein CPI-17.…”

Purinergic signalling in the urinary tract in health and disease

“…1b). Later studies have offered unequivocal support for this hypothesis (see [106]), not only in guinea-pig bladder [83,112,254,287,314,325,356,482,556,721], but also the bladders of many other species, including: mouse [4,301,682,714]; pig [253]; hamster [561]; marmoset and ferret [500]; dog [653] The prejunctional inhibition of both cholinergic and purinergic components of the nerve-mediated responses of the rat bladder by adenosine was taken as evidence in support of cotransmission ( [545]; see also [499]). Following the initial proposa1 that ATP contributed to the contractile responses of the urinary bladder to parasympathetic nerve stimulation [97], much debate followed, as indeed it did about the general concept of purinergic neurotransmission.…”

“…In a later study of the in vivo responses of the cat bladder to pelvic nerve stimulation it was concluded that purinergic transmission plays a role in the initiation of bladder contraction and perhaps in the initiation of urine flow, in contrast to cholinergic transmission that is involved in maintenance of contractile activity and flow [668]. In a recent study, evidence was presented that the purinergic component of parasympathetic cotransmission mediated Ca 2+ signals that provide the initial Ca 2+ /calmodulin activation of myosin light chain kinase in smooth muscle, while the muscarinic receptors provide supporting sustained responses [682]. Purinergic neurotransmission was impaired in myosin Va-deficient mouse bladders indicating that myosin Va plays a major role in the vesicular ATP transport from varicosities [170].…”