| Popis: |
The relationship between sarcoplasmic reticulum (SR) Ca2+ content and calsequestrin (CSQ) isoforms was investigated in human skeletal muscle. A fibre-lysing assay was used to quantify the endogenous Ca2+ content and maximal Ca2+ capacity of the SR in skinned segments of type I and type II fibres from vastus lateralis muscles of young healthy adults. Western blotting of individual fibres showed the great majority contained either all fast or all slow isoforms of myosin heavy chain (MHC), troponins C and I, tropomyosin and SERCA, and that the strontium sensitivity of the force response was closely indicative of the troponin C isoform present. The endogenous SR Ca2+ content was slightly lower in type I compared to type II fibres (0.76 ± 0.03 and 0.85 ± 0.02 mmol Ca2+ per litre of fibre, respectively), with virtually all of this Ca2+ evidently being in the SR, as it could be rapidly released with a caffeine-low [Mg2+] solution (only 0.08 ± 0.01 and |
