TOTAL CONTRACTILE PROTEIN CONTENTS AND GENE-EXPRESSION IN SKELETAL-MUSCLE IN RESPONSE TO CHRONIC ETHANOL-CONSUMPTION IN THE RAT

An investigation was carried out to determine changes in the contents of skeletal muscle myofibrillary proteins (i.e., the contractile fract ion composed principally of actin and myosin) and gene expression in s keletal muscle in response to ethanol feeding. Male Wistar rats were f ed a nutritionally complete liquid diet, which contained 35% of total calories as ethanol. Controls were pair-fed isocaloric amounts of the same diet, in which ethanol was replaced by isocaloric glucose. Total mixed and contractile protein contents of the gastrocnemius in ethanol -fed rats were rapidly reduced by ethanol feeding: a response was disc ernible as early as 1 week after the commencement of the ethanol feedi ng regimen (approx. -10%, p < 0.025 and p = 0.05 for mixed and myofibr illary proteins, respectively). At 2, 4, and 6 weeks, mixed and myofib rillary protein contents were further reduced in alcohol-fed rats, by between 12% and 22%, compared to pair-fed controls. Similar changes oc curred in the soluble (i.e., sarcoplasmic) protein fractions of skelet al muscle. At 2 weeks the composition of total messenger RNA and indiv idual messenger RNA species was measured. Total messenger RNA content per muscle was reduced by 35% (p < 0.05). Messenger RNA levels for alp ha-actin, beta-myosin heavy chain, and carbonic anhydrase III were not significantly altered. In conclusion, skeletal muscle protein content s are rapidly reduced by ethanol feeding, compared to pair fed control s, though mRNA species encoding specific isoforms of myosin and actin are not affected. It is possible that chronic ethanol feeding may sign ificantly alter the stability of mRNAs encoding other contractile prot eins, or alternatively, defects in translation may precominate. (C) 19 97 Elsevier Science Inc.