Selective loss of a plasma membrane protein associated with contraction of skeletal muscle.

Muscle proteins were labeled by incubating isolated frog sartorius muscles with [3H]- or [14C]phenylalanine. Sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis of plasma membrane fractions revealed a major protein band with an apparent molecular weight of approx. 96,000. Radioactivity in this band showed a clearly delineated decrease, relative to other bands, when previously labeled muscles were induced to contract either by electrical stimulation or by increasing the influx of Ca2+ from the incubation medium. It is postulated that a Ca2+-activated neutral protease may account for this decrease in labeled membrane protein.