Localization of protein kinase C in skeletal muscle T-tubule membranes.

Membrane fractions enriched in transverse tubules, either predominantly free or junctional, sarcoplasmic reticulum subfractions and purified sarcolemmal preparations have been isolated from rabbit skeletal muscle and examined for their contents of protein kinase C. Using activity measurements and immunoblotting methods, we have been able to detect substantial amounts of endogenous protein kinase C in T-tubules membranes and to a lesser extent, in muscle sarcolemma. Protein kinase C was found to be highest in junctional T-tubules and to be virtually absent from sarcoplasmic reticulum-derived membrane fractions. Immunofluorescence staining of muscle fibers is consistent with a T-tubule localization of the kinase. The T-tubule-associated protein kinase C enzyme phosphorylates several potentially important membrane proteins.