The modulation of Ca2+ channel density and oxidative capacity in skeletal muscle after different training protocols were studied in Atlantic salmon smolts. The effect of endurance exercise on dihydropyridine (DHP) and ryanodine (Ry) receptor densities as well as on muscle metabolism were determined by immunoblot and histochemical analysis from swimming muscles of fish subjected to nine different training protocols varying between duration and water current velocity.

In general, training caused a significant increase in the density of both receptors. In red muscle, the most notable increase in DHP and Ry receptor expression was in fish swimming against intermediate current velocity for a two-week period (182.3 ± 16.3%, 234.6 ± 30.3%, respectively). In white muscle, the expression of DHP and Ry receptors was most up-regulated after a six-week swimming period also at intermediate velocity (270.4 ± 23.9%, 114.4 ± 15.3%, respectively). As with the activity of enzymes involved in muscle energy supply, exercise resulted in an increase in succinate dehydrogenase (SDH) activity, but a decrease in the phosphorylase activity.

We conclude that the expression of both receptors was up-regulated in the swimming muscles of salmon as a consequence of training. This, along with the increased oxidative enzyme activity, provides benefits to the contraction efficiency of fish muscles while swimming. However, it was also observed that optimal oxidative swimming capacity is achieved only with a proper exercise program, since the most relevant changes in receptor expression as well as in oxidative capacity were seen in the group training with intermediate velocity.