REGULATION OF DIHYDROPYRIDINE RECEPTOR LEVELS IN SKELETAL AND CARDIAC-MUSCLE BY EXERCISE TRAINING

To examine the influence of exercise training on the expression of dih ydropyridine (DHP)-sensitive Ca2+ channels in skeletal and cardiac mus cle, we have determined DHP receptor levels by [H-3]PN200-110-binding and immunoblot analysis in homogenates and microsomal fractions of slo w-and fast-twitch muscles and heart from rats subjected to a 12-week p rogramme of moderate endurance training. We found that exercise increa ses the amount of DHP receptor in homogenates of the slow-twitch soleu s (42%) and the fast-twitch extensor digitorum longus (60%). Comparabl e increases in DHP receptor density with training were also observed i n the microsomal fractions isolated from both skeletal muscles; these increases were not due to differences in the membrane composition of t he microsomal fractions, since the relative proportion of specific enz yme markers was not affected by exercise training. Levels of DHP recep tor were not modified in cardiac muscle as a result of the exercise pr ogramme. These data suggest an up-regulation of the DHP receptor in th e skeletal muscle as a consequence of exercise training, which may pla y a role in the adaptation of skeletal muscle to increased contractile activity.