Exposure to pressure stimulus enhances succinate dehydrogenase activity in L6 myoblasts

Abstract

.-Contraction of skeletal muscle generates pressure stimuli to intramuscular tissues. However, the effects of pressure stimuli, other than those created by electricity or nerve impulse, on physiological and biochemical responses in skeletal muscles are unknown. The purpose of this study is to examine the effects of a pure pressure stimulus on metabolic responses in a skeletal muscle cell line. Atmospheric pressure was applied to L6 myoblasts using an original apparatus. Succinate dehydrogenase (SDH) activity was evaluated by colorimetric assay using tetrazolium monosodium salt. The amounts of 2-deoxy-[ 3 H]glucose uptake and lactate release were measured. SDH activity was 2.6-to 2.9-fold higher in pressurized L6 cells than in nonpressurized L6 cells (P Ͻ 0.01), and 2-deoxy-[ 3 H]glucose uptake was 2.2-fold higher (P Ͻ 0.001). In addition, the amount of released lactate decreased from 6.8 to 3.7 mol/dish when pressure was applied (P Ͻ 0.001). In contrast, the intracellular lactate contents of the pressurized cells were higher than those of nonpressurized cells (P Ͻ 0.01). However, the total amount of released lactate and intracellular lactate was lower in the pressurized cells than in nonpressurized cells. These findings demonstrate that a pure pressure stimulus enhances aerobic metabolism in L6 skeletal muscle cells and raise the possibility that elevated intramuscular pressure during muscle activity may be an important factor in stimulating oxidative metabolic responses in skeletal muscles. mechanical pressure; aerobic metabolism; lactate; glucose uptake WHEN A MUSCLE CONTRACTS, it not only receives electrical stimulation but is also subjected to mechanical forces. The mechanical forces to skeletal muscles are classified into two components: stretching and intramuscular pressure. The former stimulus is developed during elongation of muscle length by external-strain force. On the other hand, intramuscular pressure is generated by contraction (i.e., force production) of the pressure-applied muscle itself, independent of alterations in muscle length (1). The effects of stretching stimuli on metabolism, intracellular signal events, and gene expression in skeletal muscle tissues or cells have been shown (3,6,9,15,16). In those studies, passive stretching (i.e., unrelated to innervation) caused glucose uptake in isolated muscles and cultured muscle cells (6,9,16). On the basis of those reports, it appears that skeletal muscle is sensitive to mechanical forces independent of electrical stimuli and humoral factors.With regard to intramuscular pressure, Ballard et al.(1) demonstrated that the intramuscular pressures at concentric contraction during walking and running were ϳ180 and 270 mmHg, respectively. However, very little is known about the effects of a pressure stimulus as a component of mechanical forces during contraction on the physiological and biochemical responses of skeletal muscles. On the basis of the intensity of the intramuscular pressure reported by Ballard et al. and the fact that a pressure stimulus i...

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