title: Regional variation in myosin isoforms and phosphorylation at the resting tone in urinary bladder smooth muscle.
abstract: Urinary bladder filling and emptying requires coordinated control of bladder body and urethral smooth muscles. Bladder dome, midbladder, base, and urethra showed significant differences in the percentage of 20-kDa myosin light chain (LC20) phosphorylation (35.45 +/- 4.6, 24.7 +/- 2.2, 13.6+/- 2.1, and 12.8 +/- 2.7%, respectively) in resting muscle. Agonist-mediated force was associated with a rise in LC20 phosphorylation, but the extent of phosphorylation at all levels of force was less for urethral than for bladder body smooth muscle. RT-PCR and quantitative competitive RT-PCR analyses of total RNA from bladder body and urethral smooth muscles revealed only a slight difference in myosin heavy chain mRNA copy number per total RNA, whereas mRNA copy numbers for NH2-terminal isoforms SM-B (inserted) and SM-A (noninserted) in these muscles showed a significant difference (2.28 x 10(8) vs. 1.68 x 10(8) for SM-B and 0.12 x 10(8) vs. 0.42 x 10(8) for SM-A, respectively), which was also evident at the protein level. The ratio of COOH-terminal isoforms SM2:SM1 in the urethra was moderately but significantly lower than that in other regions of the bladder body. A high degree of LC20 phosphorylation and SM-B in the bladder body may help to facilitate fast cross-bridge cycling and force generation required for rapid emptying, whereas a lower level of LC20 phosphorylation and the presence of a higher amount of SM-A in urethral smooth muscle may help to maintain the high basal tone of urethra, required for urinary continence.
authors.affiliation: Division of Urology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Hypolite
authors.forename: M E
authors.initials: ME
authors.lastname: DiSanto
authors.forename: Y
authors.initials: Y
authors.lastname: Zheng
authors.forename: S
authors.initials: S
authors.lastname: Chang
authors.forename: A J
authors.initials: AJ
authors.lastname: Wein
authors.forename: S
authors.initials: S
authors.lastname: Chacko
mesh_terms: D000818:Animals; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D009130:Muscle, Smooth / Q000378:metabolism* / Q000502:physiology; D018995:Myosin Heavy Chains / Q000378:metabolism*; D018994:Myosin Light Chains / Q000378:metabolism*; D010766:Phosphorylation; D020033:Protein Isoforms / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011817:Rabbits; D014521:Urethra / Q000378:metabolism* / Q000502:physiology; D001743:Urinary Bladder / Q000378:metabolism* / Q000502:physiology
chemical_list: D018994:Myosin Light Chains; D020033:Protein Isoforms; D012333:RNA, Messenger; D018995:Myosin Heavy Chains