Effects of training on the concentration of Na+, K+‐ATPase in foal muscle

Abstract

Summary We investigated the effect of training on the Na+, K+‐ATPase concentration in foal skeletal muscle by measurement of [3H]ouabain binding. From the 7th day after birth, 12 foals were divided in 3 groups: a) staying in a box stall (Box); b) staying in a box stall with a training regimen of an increasing number of sprints per day (Training); and c) staying on pasture (Pasture). Euthanasia was performed after 5 months. In semitendinosus muscle, the concentration of [3H]ouabain binding sites (pmol/g wet wt) was 181 ± 6 in the Box, 220 ± 15 in the Training, and 197 ± 8 in the Pasture group (all n = 6; Box vs. Training, P<0.05). In gluteus medius, the concentration of [3H]ouabain binding sites was 168 ± 9 in the Box, 219 ± 12 in the Training, and 175 ± 4 in the Pasture group (all n = 6; Box or Pasture vs. Training, P<0.02). Scatchard analysis of saturation curves showed that the difference in [3H]ouabain binding sites between the 3 groups could not be ascribed to differences in the Kd for ouabain. Both for semitendinosus and gluteus medius muscle, the concentration of [3H]ouabain binding sites increased in the order Box < Pasture < Training (a total increase of around 20%). This suggests a specific effect of the amount and intensity of exercise on the Na+, K+ ‐ATPase concentration in horse skeletal muscle, and may lead to a better performance during exercise.

Specificity and reversibility of the training effects on the concentration of Na+, K+‐ATPase in foal skeletal muscle

“…Whereas training induced an increase in the Na + ,K + -pump concentration in gluteus medius and semitendinosus muscles (Suwannachot et al 1999; the present study), the Na + ,K + -pump concentration in masseter muscle was not influenced. In a previous study, Kjeldsen et al (1986) found that training a ffected the Na + , K + -pump concentration in rat extensor digitorum longus, gastrocnemius and spine muscles, but not in the diaphragm.…”

“…Separate methodological experiments were carried out to evaluate the affinity of the Na + ,K + -ATPase for [ 3 H]ouabain, and the loss of specifically bound [ 3 H]ouabain during the washout in the cold. As no major differences were found between groups in these parameters (Suwannachot et al 1999;present study), changes in [ 3 H]ouabain binding site concentration detected with the standard procedure were assumed to reflect changes in the Na + ,K + -ATPase concentration.…”

“…In the present study, we used muscle samples from 15 foals age 5 months (5 Box, 5 Training and 5 Pasture) and of 9 foals at 11 months (3 Box, 3 Training and 3 Pasture). Although the samples taken at 5 months, which were reported in a previous study (Suwannachot et al 1999), were included in the present study, we have repeated all measurements of 5 month samples in order to allow direct comparison and to exclude methodological errors in the binding assay. To minimise an error due to the variation in fibre type composition in gluteus medius (Bruce et al 1993), the muscle biopsies were all taken from the same area of the muscle immediately after the foals were subjected to euthanasia.…”

“…According to the radiochemical batch analysis of Amersham, the 95% purity of [ 3 H]ouabain gave a correction factor of 1.05 for isotope impurity. The multiplication correction factors for the loss of specifically-bound [ 3 H]ouabain during washout in cold are 1.06 (Box), 1.11 (Training) and 1.03 (Pasture) (Suwannachot et al 1999). To assess the affinity constants for [ 3 H]ouabain receptor ligand interaction in masseter muscle, samples were incubated in the concentration range of 10 -8 to 10 -6 mol/l ouabain 5 .…”

“…Studies in dogs, rats, guinea pigs and human subjects demonstrated that training improves K + -homeostasis by producing an increase in the Na + , K + -ATPase activity in the sarcolemma (Knochel et al 1985;Kjeldsen et al 1990) as well as in the total concentration of Na + , K + -pumps in various muscles, except in the diaphragm (Kjeldsen et al 1 9 8 6 ;Klitgaard and Clausen 1989;Leivseth et al 1992;Green et al 1993Green et al , 1999McKenna et al 1993;Madsen et al 1 9 9 4 ;Evertsen et al 1997). The concentration of Na + , K + -pumps in gluteus medius and s e m i t e n d i n o s u s muscles of Dutch Warmblood foals following 5 months' training was increased by 20% compared to an untrained group (Suwannachot et al 1999). Also, in adult horses, training of moderate intensity induced a 23% rise in Na + , K + -ATPase concentration in g l u t e u s muscle (McCutcheon et al 1999).…”