Urological Research

, Volume 18, Issue 5, pp 341–344 | Cite as

The proportions of fiber types in human external urethral sphincter: electrophoretic analysis of myosin

  • S. Tokunaka
  • K. Okamura
  • H. Fujii
  • S. Yachiku
Original Articles


The proportions of fast and slow myosin molecules in external urethral sphincter specimens from ten urodynamically normal male bladder carcinoma patients were estimated from the contents of fast and slow myosin light chains in two-dimensional electrophoretic gels. The percentages of fast and slow myosin molecules ranged from 5.0% to 61.4% with a mean of 35.5% and from 38.6% to 95.0% with a mean of 65.5% respectively. It is therefore concluded that the human external urethral sphincter is composed of both fast and slow muscle fibers as well as other voluntary muscles. The human external urethral sphincter is considered to be a highly fatigue-resistant muscle with a very high proportion of slow muscle fibers. In the cases studied so far, there is a great diversity in the proportions of fast and slow myosin molecules; the reason for this remains unknown.

Key words

External urethral sphincter Myosin Electrophoresis Male Human 


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Copyright information

© Springer-Verlag 1990

Authors and Affiliations

  • S. Tokunaka
    • 1
  • K. Okamura
    • 1
  • H. Fujii
    • 1
  • S. Yachiku
    • 1
  1. 1.Department of UrologyAsahikawa Medical CollegeAshikawaJapan

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