Modulation of glycogen synthesis in rat skeletal muscle by changes in cell volume.

Low, Sylvia Y.; Rennie, Michael J.; Taylor, Peter M.

doi:10.1113/jphysiol.1996.sp021594

Cited by 67 publications

(52 citation statements)

References 17 publications

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“…Keller et al (29) demonstrated in vivo in humans that cell swelling induced by hypoosmolality resulted in decreased CHO oxidation and glycogenolysis and stimulated lipolysis, while cell shrinking resulted in increased glycogenolysis. These responses to both increased and decreased cell volume appear to involve signal transduction mechanisms similar to those associated with insulin and growth factor signaling, and it has been suggested that the stimulation of glycogen synthesis by cell swelling is likely due to dephosphorylation of glycogen synthase via effects on glycogen synthase kinase-3 (39). In support of this cell volume hypothesis, in the electrolyte treatment of the present study, calculated ICFV was increased by 18% from Pre-Ex at 4 h of recovery (paired t-test P ϭ 0.038), compared with only 4% in the control treatment.…”

Section: Discussionmentioning

confidence: 99%

“…However, the concurrent changes in intracellular water, K ϩ , and glycogen content during exercise in horses has not been studied. Furthermore, cell shrinkage (as occurs with dehydration) is associated with decreased glycogen synthesis in skeletal muscle (39) and hepatocytes (21) and increased CHO oxidation and glycogenolysis (29). Therefore, it is reasonable to postulate that postexercise dehydration may be one reason why muscle glycogen replenishment is so slow in horses.…”

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Fluid and electrolyte supplementation after prolonged moderate-intensity exercise enhances muscle glycogen resynthesis in Standardbred horses

Waller¹,

Heigenhauser²,

Geor³

et al. 2009

Journal of Applied Physiology

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Waller AP, Heigenhauser GJ, Geor RJ, Spriet LL, Lindinger MI. Fluid and electrolyte supplementation after prolonged moderateintensity exercise enhances muscle glycogen resynthesis in Standardbred horses. J Appl Physiol 106: 91-100, 2009. First published October 23, 2008 doi:10.1152/japplphysiol.90783.2008.-We hypothesized that postexercise rehydration using a hypotonic electrolyte solution will increase the rate of recovery of whole body hydration, and that this is associated with increased muscle glycogen and electrolyte recovery in horses. Gluteus medius biopsies and jugular venous blood were sampled from six exercise-conditioned Standardbreds on two separate occasions, at rest and for 24 h following a competitive exercise test (CET) designed to simulate the speed and endurance test of a 3-day event. After the CETs, horses were given water ad libitum, and either a hypotonic commercial electrolyte solution (electrolyte) via nasogastric tube, followed by a typical hay/grain meal, or a hay/grain meal alone (control). The CET resulted in decreased total body water and muscle glycogen concentration of 8.4 Ϯ 0.3 liters and 22.6%, respectively, in the control treatment, and 8.2 Ϯ 0.4 liters and 21.9% in the electrolyte treatment. Electrolyte resulted in an enhanced rate of muscle glycogen resynthesis and faster restoration of hydration (as evidenced by faster recovery of plasma protein concentration, maintenance of plasma osmolality, and greater muscle intracellular fluid volume) during the recovery period compared with control. There were no differences in muscle Na, K, Cl, or Mg contents between the two treatments. It is concluded that oral administration of a hypotonic electrolyte solution after prolonged moderate-intensity exercise enhanced the rate of muscle glycogen resynthesis during the recovery period compared with control. It is speculated that postexercise dehydration may be one key contributor to the slow muscle glycogen replenishment in horses. skeletal muscle; rehydration; exercise; instrumental neutron activation analysis IN THE HORSE, BOTH short-term, high-intensity, and prolonged submaximal exercise result in dehydration, loss of water and electrolytes, and depletion of skeletal muscle glycogen (23,30,31,52,53,56). Resynthesis of muscle glycogen stores requires 48 -72 h in horses, compared with 2.5 h in rats (16) and Ͻ24 h in humans (12). Previous studies in horses have altered postexercise nutrition strategies in attempts to enhance muscle glycogen resynthesis. Despite demonstrations that intravenous infusion of large amounts of glucose (3-6 g/kg) modestly accelerated muscle glycogen replenishment (14, 17), conventional feeding strategies have not been successful (23,(53)(54)(55). Initial glycogen resynthesis rates in horses after ingestion of meals with varying soluble carbohydrate (CHO) contents ranged from ϳ8 to ϳ12 mmol⅐kg dry wt Ϫ1 ⅐h Ϫ1 for mixed and high-soluble CHO diets, respectively. In contrast, in humans, initial glycogen storage rates are ϳ40 mmol⅐kg dry wt Ϫ1 ⅐h Ϫ1when at least 5 g/kg...

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Fluid and electrolyte supplementation after prolonged moderate-intensity exercise enhances muscle glycogen resynthesis in Standardbred horses

Waller¹,

Heigenhauser²,

Geor³

et al. 2009

Journal of Applied Physiology

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“…This resultant increase in extracellular osmolarity is large and rapid and is known to result in shrinkage of erythrocytes [2,35] and non-contracting skeletal muscle [3]. It is well known that changes in skeletal muscle cell volume affect contractile function [36][37][38] and cellular metabolism [39,40], suggesting that it may be important for skeletal muscle cells to regulate cell volume.…”

Section: Role Of the Nkcc In Skeletal Muscle Cell Volume Regulationmentioning

confidence: 99%

K<sup>+</sup> Transport and Volume Regulatory Response by NKCC in Resting Rat Hindlimb Skeletal Muscle

Lindinger

Hawke

Lipskie

et al. 2002

Cell Physiol Biochem

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This study tested the hypothesis that the NKCC is involved in volume regulation, specifically regulatory volume increase (RVI), in resting skeletal muscle. Neurally and vascularly isolated rat hindlimbs were perfused with a bovine erythrocyte perfusate containing ⁴²K or ⁸⁶Rb as markers of unidirectional K⁺ flux across the sarcolemma. Compared to controls, perfusion with 120 µM bumetanide (a specific inhibitor of the NKCC) decreased J_inK by 15±2%, indicating the functional presence of the NKCC. Experiments with ouabain (to block active K⁺ transport by the Na,K ATPase) showed that the bumetanide-sensitive component of J_inK comprised 35% of the total ouabain-sensitive J_inK. Inhibition of NKCC resulted in a net loss of water by muscle. When hindlimbs were perfused with hypertonic (380 mOsm/L by addition of sucrose) perfusate for 20 min, after initially blocking K⁺ channels with 1 mM barium, J_inK rapidly (2-3 min) increased 2-fold followed by a rapid decline. This rapid, transient increase in J_inK was abolished with bumetanide, confirming that perfusion with hypertonic perfusate stimulated NKCC activity and RVI. The hypertonic perfusate also resulted in temporally associated decreases in net water uptake by muscle. It is concluded that a functional NKCC is present in mammalian skeletal muscle and that it is involved in cell volume regulation.

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“…During and after exercise there may be large changes in cell volume, secondary to osmotic pressure changes caused by metabolic activity, hydrostatic pressure changes, or by sweat loss. Alterations in cell volume induced by changes in osmolality are well known to alter the rate of glycogen synthesis in skeletal muscle (Low et al 1997a). Amino acid transport into muscles is also affected by changes in cell volume induced by manipulation of the trans-membrane osmotic gradient; skeletal muscle uptake of glutamine is stimulated by cell swelling and inhibited by cell shrinkage (Low et al 1997b), and the intracellular glutamine concentration appears to play an important role in a number of processes, including protein and glycogen synthesis (Rennie et al 1998).…”

Section: Protein Synthesis and Tissue Remodelling After Trainingmentioning

confidence: 99%

The athlete’s diet: nutritional goals and dietary strategies

Maughan

2002

Proc. Nutr. Soc.

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When talented, motivated and highly trained athletes meet for competition the margin between victory and defeat is usually small. When everything else is equal, nutrition can make the difference between winning and losing. Although the primary concern of many athletes is to supplement the diet with protein, vitamins and minerals, and a range of more exotic compounds, key dietary issues are often neglected. Athletes must establish their nutritional goals, and must also be able to translate them into dietary strategies that will meet these goals. Athletes are often concerned with dietary manipulations in the period around competition, but the main role of nutrition may be to support consistent intensive training which will lead to improved performance. Meeting energy demand and maintaining body mass and body fat at appropriate levels are key goals. An adequate intake of carbohydrate is crucial for maintaining muscle glycogen stores during hard training, but the types of food and the timing of intake are also important. Protein ingestion may stimulate muscle protein synthesis in the post-exercise period, promoting the process of adaptation in the muscles. Restoration of fluid and electrolyte balance after exercise is essential. If energy intake is high and a varied diet is consumed, supplementation of the diet with vitamins and minerals is not warranted, unless a specific deficiency is identified. Specific strategies before competition may be necessary, but this requirement depends on the demands of the sport. Generally, it is important to ensure high pre-competition glycogen stores and to maintain fluid balance. There is limited evidence to support the use of dietary supplements, but some, including perhaps creatine and caffeine, may be beneficial.

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Modulation of glycogen synthesis in rat skeletal muscle by changes in cell volume.

Cited by 67 publications

References 17 publications

Fluid and electrolyte supplementation after prolonged moderate-intensity exercise enhances muscle glycogen resynthesis in Standardbred horses

Fluid and electrolyte supplementation after prolonged moderate-intensity exercise enhances muscle glycogen resynthesis in Standardbred horses

K<sup>+</sup> Transport and Volume Regulatory Response by NKCC in Resting Rat Hindlimb Skeletal Muscle

The athlete’s diet: nutritional goals and dietary strategies

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