Rho-associated kinase plays a role in rabbit urethral smooth muscle contraction, but not via enhanced myosin light chain phosphorylation

Walsh, Michael P. and Thornbury, Keith D. and Cole, William C. and Sergeant, Gerard P. and Hollywood, Mark A. and McHale, Noel G. (2010) Rho-associated kinase plays a role in rabbit urethral smooth muscle contraction, but not via enhanced myosin light chain phosphorylation. Am J Physiol Renal Physiol . (In Press)

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The involvement of Rho-associated kinase (ROK) in activation of rabbit urethral smooth muscle contraction was investigated by examining the effects of two structurally distinct inhibitors of ROK, Y27632 and H1152, on the contractile response to electric field stimulation (EFS), membrane depolarization with KCl, and α 1 -adrenoceptor stimulation with phenylephrine. Both compounds inhibited contractions elicited by all three stimuli. The protein kinase C inhibitor, GF109203X, on the other hand, had no effect. Urethral smooth muscle strips were analysed for phosphorylation of three potential direct or indirect substrates of ROK: (i) myosin regulatory light chains (LC 20 ) at S19; (ii) the myosin targeting subunit of myosin light chain phosphatase, MYPT1, at T697 and T855; and (iii) cofilin at S3. The following results were obtained: (i) under resting tension, LC 20 was phosphorylated to 0.65 ± 0.02 mol P i /mol LC 20 (n = 21) at S19; (ii) LC 20 phosphorylation did not change in response to KCl or phenylephrine; (iii) ROK inhibition had no effect on LC 20 phosphorylation in the absence or presence of contractile stimuli; (iv) under resting conditions, MYPT1 was partially phosphorylated at T697 and T855 and cofilin at S3; (v) phosphorylation of MYPT1 and cofilin was unaffected by KCl or phenylephrine; and (vi) KCl- and phenylephrine-induced contraction-relaxation cycles did not correlate with actin polymerization-depolymerization. We conclude that ROK plays an important role in urethral smooth muscle contraction, but not via inhibition of MLCP or polymerization of actin.

Item Type: Article
Uncontrolled Keywords: Urethra; Urinary continence; Myosin light chain phosphatase; Cofilin; Rho-associated kinase (ROK); Muscle, smooth
Subjects: Science
Research Centres: Smooth Muscle Research Centre
Depositing User: Concepta Woods
Date Deposited: 26 Nov 2011 12:17
Last Modified: 11 Nov 2014 16:10

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