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An Automated Technique for Simultaneous Determinations of Muscle Fiber Number and Diameter¹

University of Minnesota, St. Paul 55108

Abstract

An automated method has been developed which simultaneously determines by use of a Coulter Counter total fiber number and diameter distributions in a muscle transverse section. Formalin-fixed muscle from mouse and rat biceps brachii, rat soleus, and pig flexor digiti V brevis was frozen in embedding media, and thick (68 µm) sections were cut in a cryostat. Fibers were isolated by repeated expulsion from an automated syringe under high pressure onto a nylon mesh screen. Following isolation, the fibers were sized and counted with a model ZB Coulter Counter equipped with an accessory Coulter Channelyzer. Total fiber number and mean fiber diameter from consecutive transverse sections of the same muscle were compared using the Coulter Counter method and direct microscopic measurement.

Mean fiber diameter of 15 biceps brachii muscles from the rat was 35.4 µm as determined by the Coulter Counter method and 35.0 µm as determined by measurements with the microscope. This difference was not significant (P>.05). The correlation coefficient for the two methods of diameter determination was .96 (P<.01). Average fiber number for mouse biceps brachii, rat biceps brachii, rat soleus and pig flexor digiti V brevis, as determined by the Coulter Counter method, was respectively 2,313, 7,264, 2,435 and 6,106. The average number of fibers for the respective muscles as determined by counts with the microscope was 2,297, 7,307, 2,403 and 5,832. The only counts which were different (P<.05) were those for the pig muscle. Correlation coefficients for fiber number as determined by the two methods ranged from .70 to .99, all of which were significant (P<.05). The main advantages of the Coulter Counter technique are that it is rapid and accurate, and samples a much larger portion of the fiber population than existing techniques.

¹ Paper No. 10,041, Scientific Journal Series, Minnesota Agricultural Experiment Station, St. Paul.

² Department of Animal Science.

³ Department of Food Science and Nutrition.

⁴ The authors are indebted to Dr. D. B. Anderson and Dr. D. K. Layman for their review and suggestions related to this manuscript, and to Mr. R. Lepley for assistance with the mathematical integration.