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J Muscle Res Cell Motil (2013) 34:211231 DOI 10.1007/s10974-013-9346-9
ORIGINAL PAPER
Complex tropomyosin and troponin T isoform expression patterns in orbital and global bers of adult dog and rat extraocular muscles
Sabahattin Bicer Peter J. Reiser
Received: 14 February 2013 / Accepted: 2 May 2013 / Published online: 23 May 2013 Springer Science+Business Media Dordrecht 2013
Abstract We reported marked differences in the myosin heavy and light chain (MHC and MLC) isoform composition of fast and slow bers between the global and orbital layers of dog extraocular muscles. Many dog extraocular bers, especially orbital bers, have MHC and MLC iso-form patterns that are distinct from those in limb skeletal muscles. Additional observations suggested possible differences in the tropomyosin (Tm) and troponin T (TnT) isoform composition of global and orbital bers. Therefore, we tested, using SDS-PAGE and immunoblotting, whether differences in Tm and TnT isoform expression do, in fact, exist between global and orbital layers of dog and rat EOMs and to compare expression patterns among identied fast and slow single bers from both muscle layers. The Tm isoforms expressed in global fast and slow bers are the same as in limb fast (a-Tm and b-Tm) and slow (c-Tm and b-Tm) bers, respectively. Orbital slow orbital bers, on the other hand, each co-express all three sarcomeric Tm isoforms (a, b and c). The results indicate that fast global and orbital bers express only fast isoforms of TnT, but the relative amounts of the individual isoforms are different from those in limb fast muscle bers and an abundant fast TnT isoform in the orbital layer was not detected in fast limb muscles. Slow bers in both layers express slow TnT isoforms and the relative amounts also differ from those in limb slow bers. Unexpectedly, signicant amounts of cardiac TnT isoforms were also detected in slow bers, especially in the orbital layer in both species. TnI and TnC isoform patterns are the same as in fast and slow bers in limb muscles. These results
expand the understanding of the elaborate diversity in contractile protein isoform expression in mammalian extraocular muscle bers and suggest that major differences in calcium-activation properties exist among these bers, based upon Tm and TnT isoform expression patterns.
Keywords Tropomyosin Troponin-T Isoforms
Thin lament Calcium-regulation...