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Laboratoire de Physiologie des Interactions, Service Central de Physiologie Clinique, Hôpital A de Villeneuve, 34295 Montpellier cedex 5, France
The effect of a single bout of exhaustive exercise on muscle
lactate transport capacity was studied in rat skeletal muscle sarcolemmal (SL) vesicles. Rats were assigned to a control
(C) group (n = 14) or an acutely
exercised (E) group (n = 20). Exercise consisted of treadmill running (25 m/min, 10% grade) to exhaustion. SL
vesicles purified from C and E rats were sealed because of sensitivity
to osmotic forces. The time course of 1 mM lactate uptake in
zero-trans conditions showed that the
equilibrium level in the E group was significantly lower than in the C
group (P < 0.05). The initial rate
of 1 mM lactate uptake decreased significantly from 2.44 ± 0.22 to
1.03 ± 0.08 nmol · min
1 · mg
protein1
(P < 0.05) after exercise, whereas
that of 50 mM lactate uptake did not differ significantly between the
two groups. For 100 mM external lactate concentration
([lactate]), exhaustive exercise increased initial rates of
lactate uptake (219.6 ± 36.3 to 465.4 ± 80.2 nmol · min1 · mg
protein1,
P < 0.05). Although saturation
kinetics were observed in the C group with a maximal transport velocity
of 233 nmol · min1 · mg
protein1 and a
Michealis-Menten constant of 24.5 mM, saturation properties were not
seen after exhaustive exercise in the E group, because initial rates of
lactate uptake increased linearly with external [lactate].
We conclude that a single bout of exhaustive exercise significantly
modified SL lactate transport activity, resulting in a decrease in 1 mM
lactate uptake and was associated with alterations in the saturable
properties at [lactate] above 50 mM. These results suggest
that changes in sarcolemmal lactate transport activity may alter
lactate and proton exchanges after exhaustive exercise.
isolated membrane; carrier-mediated transport; glycogen; treadmill exercise; monocarboxylate transporter; pH
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