Enhanced technique to measure proteins in single segments of human skeletal muscle fibers: fiber-type dependence of AMPK-alpha1 and -beta1.

Human physiological studies typically use skeletal muscle biopsies from the heterogeneous vastus lateralis muscle comprised of both fast-twitch and slow-twitch fiber types. It is likely that potential changes of physiological importance are overlooked because fiber-type specific responses may not be apparent in the whole muscle preparation. A technological advance in Western blotting is presented where proteins are analyzed in just one small segment (<2 mm) of individual fibers dissected from freeze-dried muscle samples using standard laboratory equipment. A significant advance is being able to classify every fiber at the level of both contractile (myosin heavy chain and tropomyosin) and sarcoplasmic reticulum [sarco(endo)plasmic reticulum Ca(2+)-ATPase type 1] properties and then being able to measure specific proteins in the very same segments. This removes the need to fiber type segments before further analyses and, as such, dramatically reduces the time required for sample collection. Compared with slow-twitch fibers, there was less AMP-activated protein kinase (AMPK)-α(1) (∼25%) and AMPK-β(1) (∼60%) in fast-twitch fibers from human skeletal muscle biopsies.