Lactate uptake by skeletal muscle sarcolemmal vesicles decreases
after 4 weeks of hindlimb unweighting in rats.
H., Dubouchaud, Granier P., Mercier J., Le Peuch C., Pr[acute]efaut
Ch.
Laboratoire de Physiologie des Interactions, Service d'Exploration
de la Fonction Respiratoire, H[circumflex]opital A. de Villeneuve,
371, Avenue du Doyen G. Giraud, 34295 MONTPELLIER cedex 5, FRANCE,
Centre de Recherche en Biochimie Macromol[acute]eculaire, CNRS UPR
9008, INSERM U 249, BP 5051, 34033 MONTPELLIER, FRANCE
APStracts 2:0423A, 1995.
We investigated the effects of four weeks of hypodynamia on the rate
of lactate transport in skeletal muscle sarcolemmal vesicles from
control (C) and hindlimb suspended (S) rats. Characterization of the
sarcolemmal preparations was achieved using marker enzyme (K+-para
-nitrophenylphosphatase) and measurement of 1 mM U14C-lactate
transport activity under zero-trans conditions with or without pH
-gradient or transport inhibitor -hydroxycinnamate (-CHC).
Preparations from the two groups were not significantly different
concerning yield and purification. Based on these results, we used
this model to analyze the lactate transport activity after
hypodynamia by tail suspension. Hindlimb suspension caused a shift
from slow to fast myosin heavy chain (MHC) isoforms in soleus muscles
with a 40 % decrease in the citrate synthetase activity (35.3
[mu]mol.g-1.min-1 21.4 [mu]mol.g-1.min-1 2.1, p<0.05). 1 mM
lactate uptake in vesicles from the two groups was a function of time
and the rate after hindlimb suspension was significantly decreased in
S compared to C (2.25 +/- 0.44 nmol.min-1.mg protein-1 vs 3.50 +/-
0.26 nmol.min-1.mg protein-1, respectively, p<0.05). These
differences were not observed for a higher lactate concentration (50
mM). These results suggest that the level of physical activity plays
a role in the regulation of sarcolemmal lactate transport activity
implicated in the exchanges of lactate between producing and
utilizing cells, organs and tissues, which is a major way of
carbohydrate energy distribution in humans and others species.
Received 31 March 1995; accepted in final form 22 September 1995.
APS Manuscript Number A361-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 6 November 95