Myosin heavy chain composition of rat middle ear muscles.
OBJECTIVE
To quantitatively analyze myosin heavy chain (MHC) mRNA composition in two rat middle ear muscles (the tensor tympani and stapedius) using competitive polymerase chain reaction (PCR).


METHODS
An exogenous template, including oligonucleotide sequences specific for the seven rat MHCs (2A, 2B, 2X, 2L/EOM, embryonic, neonatal and beta-cardiac) as well as beta-actin, was constructed and used as the competitor.


RESULTS
The tensor tympani and stapedius contained all MHC isoforms except 2L. The tensor tympani contained approximately equal proportions of 2X (40.4% +/- 6.5%) and 2A (34.0% +/- 1.3%) MHCs, with a smaller percentage of 2B (16.6% +/- 1.5%) and neonatal (7.5% +/- 0.6%) MHCs, while beta-cardiac and embryonic MHCs were minimally expressed. The stapedius contained predominantly 2X (58.0% +/- 4.2%) and 2A (32.3% +/- 6.7%) MHCs, with a smaller percentage of 2B (7.4% +/- 0.2%) and beta-cardiac (1.9% +/- 0.1%) MHCs. Neonatal and embryonic MHCs were detected at very low levels.


CONCLUSIONS
These results suggest that two middle ear muscles, which are mainly composed of two fast-twitching myosins (2X and 2A MHCs), contract fast and are fatigue-resistant.
Jung
Hak Hyun
HH
Department of Otolaryngology-Head and Neck Surgery, University of Ulsan College of Medicine, Seoul, South Korea.
Han
Seung Hoon
SH
Nam
Soon Yuhl
SY
Kim
Young Ho
YH
Kim
Jeung Lim
JL
D000199:Actins / Q000378:metabolism; D000818:Animals; D018076:DNA, Complementary / Q000032:analysis; D004432:Ear, Middle / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D018995:Myosin Heavy Chains / Q000235:genetics / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D013198:Stapedius / Q000378:metabolism*; D013719:Tensor Tympani / Q000378:metabolism*
D000199:Actins; D018076:DNA, Complementary; D012333:RNA, Messenger; D018995:Myosin Heavy Chains