Regulation of dihydropyridine receptor levels in skeletal and cardiac muscle by exercise training.

To examine the influence of exercise training on the expression of dihydropyridine (DHP)-sensitive Ca2+ channels in skeletal and cardiac muscle, we have determined DHP receptor levels by [3H]PN200-110-binding and immunoblot analysis in homogenates and microsomal fractions of slow- and fast-twitch muscles and heart from rats subjected to a 12-week programme of moderate endurance training. We found that exercise increases the amount of DHP receptor in homogenates of the slow-twitch soleus (42%) and the fast-twitch extensor digitorum longus (60%). Comparable increases in DHP receptor density with training were also observed in the microsomal fractions isolated from both skeletal muscles; these increases were not due to differences in the membrane composition of the microsomal fractions, since the relative proportion of specific enzyme markers was not affected by exercise training. Levels of DHP receptor were not modified in cardiac muscle as a result of the exercise programme. These data suggest an up-regulation of the DHP receptor in the skeletal muscle as a consequence of exercise training, which may play a role in the adaptation of skeletal muscle to increased contractile activity.