Polyadenylated rna, actin mrna, and myosin heavy chain mrna in
young and old human skeletal muscle.
Welle, Stephen, Kirti Bhatt, and Charles Thornton.
Departments of Medicine, Neurology, and Physiology, University of
Rochester
APStracts 2:0187E, 1995.
The myofibrillar protein synthesis rate in old human skeletal muscle
is slower than that in young adult muscle. To examine whether this
difference in protein synthesis rate is explained by reduced
availability of the mRNAs that encode the most abundant myofibrillar
proteins, we determined relative hybridization signals from probes
for actin mRNA, myosin heavy chain mRNA, and total polyadenylated RNA
in vastus lateralis muscle biopsies taken from young (22-31 years
old) and old (61-74 years old) human subjects. The mean fractional
rate of myofibrillar synthesis was 38% slower in the older muscles,
as determined by incorporation of a stable isotope tracer. Total
actin and myosin heavy chain mRNAs, and polyadenylated RNA, were
determined using slot blot assays. Isoform-specific determinations of
[alpha]-actin mRNA, type I myosin heavy chain mRNA, and type IIa
myosin heavy chain mRNA were done with ribonuclease protection
assays. Hybridization signals were expressed relative to tissue DNA
content. There was no difference between age groups in total
polyadenylated RNA, or in any of the specific mRNAs. We conclude that
the slower myofibrillar synthesis rate in older muscle is not caused
by reduced mRNA availability.
Received 5 July 1995; accepted in final form 24 August 1995.
APS Manuscript Number E309-5.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 September 1995.