EXPRESSION OF ACETYLCHOLINE-RECEPTOR MESSENGER-RNAS IN ATROPHYING ANDNONATROPHYING SKELETAL-MUSCLES OF OLD RATS

We examined the age-related association in skeletal muscle between atr ophy and expression of mRNAs encoding both the gamma-subunit of the ni cotinic acetylcholine receptor (AChR), and myogenin, a transcription f actor that upregulates expression of the gamma-subunit promoter. Gastr ocnemius and biceps brachii muscles were collected from young (2-mo-ol d), adult (18-mo-old), and old (31-mo-old) Fischer 344/Brown Norway F1 generation cross male rats. In the gastrocnemius muscles of old vs. y oung and adult rats, lower muscle mass was accompanied by significantl y elevated AChR gamma-subunit and myogenin mRNA levels. In contrast, t he biceps brachii muscle exhibited neither atrophy nor as drastic a ch ange in AChR gamma-subunit and myogenin mRNA levels with age. Expressi on of the AChR E-subunit mRNA did not change with age in either gastro cnemius or biceps brachii muscles. Thus changes in skeletal muscle ACh R gamma-subunit and myogenin mRNA levels may be more related to atroph y than to chronological age in old rats.