The principal objectives of this study were to ascertain if the vastus medialis
(VM) responded to microgravity exposure. Three approaches were used: 1) a histochem-
ical evaluation of cellular morphology (fibers and capillaries); 2) an assessment
of biochemical composition (protein, RNA and DNA concentrations) and 3) an estimation
of metabolic activities and capacities (oxidative and glycolytic metab- olism).
Frozen muscle sections were stained for ATPase activity; muscle fibers and
capil- laries were differentiated. Fiber area and density measurements were
made, and capillary distribution was assessed. The remaining samples were lyophilized,
weighed, and powdered. Aliquots were used for protein; RNA and DNA concen- tration
determinations; and for lactate dehydrogenase(LDH), citrate synthase (CS) activities,
and lipoprotein lipase (LPL) activities.
Although some of the morphological parameters suggest a small degree of atrophy
in the VM, the biochemical analysis (protein, RNA, and DNA) suggest that these
may be minimal and functionally nonsignificant. The relatively similar CS and
LDH activities of VM from flight and various control groups, as well as the
lack of difference between flight and synchronous rats, suggest that there is
little or no effect on the oxidative or glycolytic function of this muscle.
Since the VM is chiefly a mixed fast twitch muscle, these metabolic indices
of energy production are relatively unchanged. The results of this study are
in agreement with previous observations of another type II fast twitch muscle,
the extensor digitorum longus, from Spacelab-3 rats which did not respond markedly
to weightlessness and whole body suspension.
Musacchia, X.J. et al.: Biochemical and Histochemical Observations of Vastus
Medialis. Final Reports of the U.S. Experiments Flown on the Soviet Biosatellite
Cosmos 1887. J.P. Connolly, R.E. Grindeland, and R.W. Ballard, eds., NASA TM-102254,
1990, pp. 207-214.
Musacchia, X.J. et al.: Biochemical and Histochemical Observations of Vastus
Medialis from Rats Flown in Cosmos 1887. Physiologist, supl., vol. 32, no. 1,
1989, pp. S21-S22.
Steffen, J.M. and X.J. Musacchia: Effect of Hypokinesia and Hypodynamia on
Protein, RNA and DNA in Rat Hindlimb Muscles. American Journal of Physiology,
vol. 247, 1984, pp. R728-R732.¥
¥ = publication of related ground-based study