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The Journal of Experimental Biology 204, 4237-4248 (2001)
© 2001 The Company of Biologists Limited

Identification of myosin light chains in Rana pipiens skeletal muscle and their expression patterns along single fibres

Gordon J. Lutz^*, Shannon N. Bremner, Michael J. Bade and Richard L. Lieber

Departments of Orthopaedics and Bioengineering, Biomedical Sciences Graduate Group, University of California, Veterans Affairs Medical Center and Veterans Medical Research Foundation, 3350 La Jolla Village Drive, San Diego, CA 92161, USA

*Author for correspondence at Department of Orthopaedics, University of California San Diego School of Medicine, Veterans Affairs Medical Centers (9151), 3350 La Jolla Village Drive, San Diego, CA 92161 USA (e-mail: glutz{at}ucsd.edu).

Accepted 1 October 2001

Isoforms of myosin heavy chain (MHC) and myosin light chain (MLC) influence contractile kinetics of skeletal muscle. We previously showed that the four major skeletal muscle fibre types in Rana pipiens (type 1, type 2, type 3 and tonic; amphibian nomenclature) contain four unique MHC isoforms. In the present study we defined the MLCs expressed in each of these R. pipiens fibre types. The MLC composition of single MHC-typed fibres was determined from western blots using a panel of monoclonal MLC antibodies. A total of seven MLCs were identified, including four types of MLC1, two of MLC2 and a single MLC3. Twitch fibre types (types 1, 2 and 3) expressed MLC1_f and MLC2_f, while tonic fibres contained a unique set of isoforms, MLC1_Ta, MLC1_Tb and MLC2_T. MLC3 was expressed primarily in type 1, type 1-2 and type 2 fibres. Surprisingly, some frogs displayed a striking pattern of MLC expression where a unique isoform of MLC1 (MLC1_x) was coexpressed along with the normal MLC1 isoform(s) in all fibre types. MLC1_x was either expressed in all fibres of a given frog or was completely absent. The intraspecific polymorphism in MLC1 expression is likely to have a genetic basis, but is unlikely to be caused by allelic variation. The ratio of MLC3/MLC1 increased in direct proportion to the percentage of type 1 MHC, but was only weakly correlated. The variability in MLC3/MLC1 within a fibre type was extremely large. Both the MHC isoform and MLC3/MLC1 ratio varied significantly between 1 mm segments along the length of fibres. For all segments combined, MLC3/MLC1 increased with the percentage of type 1 MHC, but the correlation between segments was weaker than between fibres.

Key words: frog, Rana pipiens, fibre type, skeletal muscle, electrophoresis, contractile protein, isoform.

This article has been cited by other articles:

				T. J. Patel, R. Das, J. Friden, G. J. Lutz, and R. L. Lieber Sarcomere strain and heterogeneity correlate with injury to frog skeletal muscle fiber bundles J Appl Physiol, November 1, 2004; 97(5): 1803 - 1813. [Abstract] [Full Text] [PDF]

				G. J. Lutz, S. R. Sirsi, S. A. Shapard-Palmer, S. N. Bremner, and R. L. Lieber Influence of myosin isoforms on contractile properties of intact muscle fibers from Rana pipiens Am J Physiol Cell Physiol, April 1, 2002; 282(4): C835 - C844. [Abstract] [Full Text] [PDF]