Biochemical and Histological Studies on the Possible Mechanism of Mouse Muscular Hypotrophy

The homo-type(dy/dy)and hetero-type(dy/？)Of male C57BL/6J-dy mice(5-6wks and 8-9wks old)were used to elucidate biochemically and histologically the possible mechanism of non-exercise muscular hypotrophy.Whole hindlimb muscles were minced with scissors，and homogenized with 25 mM phosphate buffer(pH7.4)at 0°C.The homogenate was fractionated into buffer-soluble(F-1)，1.2M KCl-soluble(F-2)，1.2M KCl-insoluble(F-3)，ribonucleic acid(RNA)，deoxyribonucleic acid(DNA)and protein.Serial cross section(10&lt；mu&gt；m thick)of paraffin embedded M.gasrocnemius and M.soleus were stained with hematoxylin and eosin.The numbers of nucleus and muscle fiber per unit area(&lt；1 mm^2&gt；)and the area of cross section of muscle fiber were determined。1)。[DNA]and[RNA]of hindlimb muscles in dy/dy mice was 2.5-2.8times and 1.5-1.8 times higher than that in dy/？Mice，respectively。Each nucleic acid concentration decreased significantly by muscular hypotrophy.2)。[protein]of the muscle tissue in dy…More/dy mice was 1.22times lower than that in dy/？Mice.3)。Apparent muscle cell volume in dy/dy mice estimated from[protein]/DNA and muscle weight/DNA，was 7.9times and 3.0-3.4times lower than those in dy？Mice，respectively。4)。The order of decrease of protein contents in each muscle fraction by muscle hypotrophy was F-2&gt；F-3&gt；F-1，indicating that the decrease of protein content is not identical with each fraction。5)。Electrophoretic pattern of muscle proteins in each fraction was changed drastically by muscle hypotrophy，indicating that the hypotrophy changes the fractional composition ratio of muscle proteins.6)。The numbers of nucleus in dy/dy mice was1.9times larger than that in dy/？Mice.7)。The ratio of the number of centronucleus to total numbers of nucleus in dy/dy mice was 9.5times larger than that in dy/？Mice.8)。Area frequency distribution of muscles in dy/dy mice deviated from the normal distribution profile in dy/？Mice.The mean area(0.0049&lt；mm^2&gt；)of the cross section in dy/dy mice was 0.68times smaller than that(0.0072&lt；mm^2&gt；)in dy/？Mice.9)。The possible mechanism of muscle hypotrophy was discussed in detail.Less：Less

The homo-type(dy/dy) and hetero-type(dy/?) of male C57BL/6J-dy mice(5-6 wks and 8-9 wks old) were used to elucidate biochemically and histologically the possible mechanism of non-exercise muscular hypotrophy. Whole hindlimb muscles were minced with scissors, and homogenized with 25mM phosphate buffer(pH 7.4) at 0゜C. The homogenate was fractionated into buffer-soluble(F-1), 1.2M KCl-soluble(F-2), 1.2M KCl-insoluble(F-3), ribonucleic acid(RNA), deoxyribonucleic acid(DNA) and protein. Serial cross section(10 <mu> m thick) of paraffin embedded M. gasrocnemius and M. soleus were stained with hematoxylin and eosin. The numbers of nucleus and muscle fiber per unit area( <1mm^2> ) and the area of cross section of muscle fiber were determined. 1). [DNA] and [RNA] of hindlimb muscles in dy/dy mice was 2.5-2.8 times and 1.5-1.8 times higher than that in dy/? mice, respectively. Each nucleic acid concentration decreased significantly by muscular hypotrophy. 2). [protein] of the muscle tissue in dy … More /dy mice was 1.22 times lower than that in dy/? mice. 3). Apparent muscle cell volume in dy/dy mice estimated from [protein]/DNA and muscle weight/DNA, was 7.9 times and 3.0-3.4 times lower than those in dy? mice, respectively. 4). The order of decrease of protein contents in each muscle fraction by muscle hypotrophy was F-2>F-3>F-1, indicating that the decrease of protein content is not identical with each fraction. 5). Electrophoretic pattern of muscle proteins in each fraction was changed drastically by muscle hypotrophy, indicating that the hypotrophy changes the fractional composition ratio of muscle proteins. 6). The numbers of nucleus in dy/dy mice was 1.9 times larger than that in dy/? mice. 7). The ratio of the number of centronucleus to total numbers of nucleus in dy/dy mice was 9.5 times larger than that in dy/? mice. 8). Area frequency distribution of muscles in dy/dy mice deviated from the normal distribution profile in dy/? mice. The mean area(0.0049 <mm^2> ) of the cross section in dy/dy mice was 0.68 times smaller than that(0.0072 <mm^2> ) in dy/? mice. 9). The possible mechanism of muscle hypotrophy was discussed in detail. Less