The Gene Expression Of Myosin Heavy Chain Isoforms In Striated Urinary Sphincter Muscle Of Female Rats

Objective: Urinary sphincter system is the main morphological basis responsible for the urinary continence in mammals. And the striated muscle fibers that covered outside the urethral wall is the most important component that comprise the urinary sphincter system. The urinary sphincter system posses complicated and precise function in order to meet the diverse requirements of urinary continence in the daily life. In this study we detected the composition of myosin heavy chain isoforms of striated urinary sphincter in normal female rats to better understand how the urinary sphincter system works in maintaining urinary continence.Methods: The urinary sphincter tissue specimens were taken from 12 adult female F344 rats under anesthesia. The total RNA was extracted from the samples by using the TRIzol reagent following the company protocol. Expressions of myosin heavy chain isoforms of striated urinary sphincter were detected by reverse transcriptase - polymerase chain reaction (RT-PCR).Results: Four types of mRNA of myosin heavy chain isoforms were detected in striated urinary sphincter in normal adult female rats, where MHC-Ⅱb account for the highest level (38.1±0.7)% of total detectable OD,MHC-Ⅱaccount for the second level (34.6±0.8)% of total detectable OD,MHC-Ⅱx account for the third level (18.1±1.2)% of total detectable OD and MHC-Ⅰaccount for the lowest level (9.2± 0.4)% of total detectable OD.Conclusion: All four myosin heavy chain isoforms are expressed in the striated urinary sphincter in normal adult female nonporous rats, which demonstrates that the striated urinary sphincter consists of four types of fibers: typeⅠ(slow switch fiber), typeⅡa (fast switch fatigue resistant fiber), typeⅡb (fast fatigabl fiber) and typeⅡx (super fast fiber). The diversity of fiber types in the urinary sphincter is the molecular basis for its complicated and precise function in maintaining urinary continence.