The ratio between intrinsic 115 kDa and 30 kDa peptides as a marker of fibre type-specific sarcoplasmic reticulum in mammalian muscles.

Sarcoplasmic reticulum displays characteristic differences in Ca2+-uptake, Ca2+-ATPase and the pattern of membrane proteins in type I, IIA and IIB fibres. The ratio between the 115 kDa Ca2+-ATPase and a 30 kDa protein is of characteristic magnitude in the sarcoplasmic reticulum of the three fibre types in rat muscles. The slow-to-fast fibre type transformation observed in rabbits during chronic nerve stimulation is accompanied by predictable changes of this ratio.