Aims: 

Sarcoplasmic and t-tubule membrane proteins of skeletal muscle regulate intracellular Ca²⁺concentration and play central role in muscle contraction and relaxation. The purpose of this study was to evaluate the effects of short intense (SHO) and prolonged moderate (PRO) stimulations on mRNA expression of receptor proteins involved in Ca²⁺regulation.

Methods: 

mRNA levels of dihydropyridine (Cacna1) and ryanodine (Ry1) receptor, Ca²⁺-ATPase (SERCa1), and calsequestrin (CASQ1,2) in extensor digitorum longus (EDL) and soleus (SOL) muscles of rat were assessed by RT-PCR after in vitro stimulation (SHO: 60 Hz, 5 min; PRO: 20 Hz, 40 min) followed by a 300 min recovery period.

Results: 

In general, stimulation decreased mRNA expression of all proteins studied. Most prominent down-regulation (p < 0.01) in relation to resting control was observed for Cacna1 mRNA content (19% after SHO in EDL; 21 and 24% after SHO and PRO in SOL). A significant decrease (p < 0.05) was seen also for Ry1 mRNA content (45% after PRO in SOL), SERCa1 (27% after SHO in SOL), CASQ1 (15% after SHO in EDL), and CASQ2 (65% after SHO in EDL, 55% after PRO in SOL).

Conclusion: 

These results demonstrate contraction-induced mRNA responses of the main components of Ca²⁺regulating system in rat skeletal muscle. The decreased mRNA levels of fast isoforms Cacna1, Ry1, SERCa1 and CASQ1 in slow-twitch SOL, and the slow isoform CASQ2 in fast-twitch EDL may contribute to phenotypic adaptations in response to muscle contractions. Furthermore, the results suggest that down-regulation of Ca²⁺regulating proteins may be a mechanism explaining at least partly the long-lasting fatigue involved in the muscle dysfunction and pain.