Slow/cardiac sarcoplasmic reticulum Ca2+-ATPase and phospholamban mRNAs are expressed in chronically stimulated rabbit fast-twitch muscle


  • This study was supported by grants from the Deutsche Forschungsgemeinschaft, Sonderforschungsbereich 156, and from the Medical Research Council of Canda, the Muscular Dystrophy Association of Canda, and the Heart and Stroke Foundation of Ontario. E. L. was a postdoctoral fellow of the Muscular Dystrophy Association (USA). The authors thank Ms. Sara Krüger and Ms. Stella deLeon for excellent technical assistance.

Correspondence to D. Pette, Fakultät für Biologie, Universität Konstanz, Postfach 5560, D-7750 Konstanz Republic of Germany


Fast-twitch extensor digitorum longus muscles of the rabbit were subjected to chronic low-frequency stimulation during different time periods. Changes in the relative amounts of mRNAs encoding fast and slow/cardiac Ca2+ -ATPase isoforms were assessed through the use of an R Nase-protection assay. Stimulation-induced increases in slow/cardiac Ca2+ -ATPase and phospholamban mRNAs were quantified by mRNA hybridization. Prolonged stimulation resulted in an exchange of the fast with the slow/cardiac Ca2+ -ATPase isoform mRNAs. The exchange was complete after 72 d of stimulation as compared with normal slow-twitch soleus muscle. The tissue content of phospholamban mRNA reached levels similar to that found in normal slow-twitch soleus muscle by the same time. The conversion of the sarcoplasmic reticulum coincided with the fast-to-slow troponin C isoform transition, previously investigated in the same muscles.