The effect of thyrotoxicosis on the capacity of fragmented sarcoplasmic reticulum (FSR) and crude homogenate (CH) to sequester Ca2+ was determined in rat muscle for the slow-twitch type I soleus (SOL), the fast-twitch type IIA deep region of the vastus lateralis (DVL), and the fast-twitch type IIB superficial region of the vastus lateralis (SVL). The maximal rate of Ca2+ uptake (V(max)) and K(m) were determined in both the CH and FSR preparations, and the total Ca2+ uptake capacity of the CH was determined. In the slow SOL, thyrotoxicosis increased the V(max) (8.20 ± 0.96 vs. 15.70 ± 0.92 μmol Ca2+.g wet muscle-1.min-1) and the total Ca2+ uptake (17.62 ± 1.30 vs. 27.13 ± 2.16 μmol Ca2+.g wet muscle-1) of the CH preparation. Thyrotoxicosis increased the FSR yield 2.3-fold in the slow-twitch SOL; however, the kinetic characteristics (V(max) and K(m)) of these vesicles were not altered. Thyrotoxicosis had no effect on the CH and FSR preparations in either the type IIA or type IIB sample. These results can be explained by a thyroid hormone-mediated increase in the quantity of the sarcoplasmic reticulum in type I muscle and suggest no effect of the hormone on the qualitative nature of the Ca2+-enzyme interaction.
|Original language||English (US)|
|Journal||American Journal of Physiology - Cell Physiology|
|State||Published - Jan 1 1982|
ASJC Scopus subject areas
- Cell Biology