Expression of specific Ca2+ regulating proteins in skeletal muscle of reindeer (Rangifer tarandus tarandus) during moderate weight loss and wintertime adaptation

Energy deprivation during the wintertime poses a challenge to skeletal muscle function. The objective of the present study was to determine the expression of specific calcium (Ca2+) regulating proteins in skeletal muscle of the reindeer during wintertime adaptation and moderate weight loss. To assess the possible changes in the dihydropyridine receptor (Cacna1), ryanodine receptor (RyR1), sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA1) and calsequestrin 1 (CASQ1) proteins, six mature female reindeer were held under experimental outdoor conditions with limited energy intake and muscle biopsies were taken from m. semitendinosus. In addition, muscle biopsies from m. semitendinosus and m. gluteus medius taken from freely ranging reindeer after slaughter (October, n = 7; January, n = 7) were included in the study. The muscle samples were analysed by Western blot. The animals lost 10–21% of their body mass (BM) during the restricted feeding, with no change in the muscle total protein content. In general, the concentrations of nearly all Ca2+ regulating components measured were maintained as a response to restricted feeding in experimental and freely ranging reindeer. Interestingly, the expression of Cacna1 was 2.3-fold up-regulated after the restricted feeding period in the m. semitendinosus of the experimental reindeer. On the contrary, in freely ranging animals, the expression of SERCA1 and RyR1 decreased 3.5- and 3.2-fold, respectively, in January compared to October. To conclude, the expression of Ca2+ regulating proteins is not altered during moderate weight loss and winter adaptation in order to maintain effective muscle contraction capacity. Up-regulation of Cacna1, however, indicates the ability to allocate Ca2+ cycling capacity to both oxidative and glycolytic metabolic pathways during times of energy deprivation.