Two populations of beta-spectrin in rat skeletal muscle.

We use immunoblotting, immunoprecipitation, and centrifugation in sucrose density gradients to show that the product of the erythrocyte beta-spectrin gene in rat skeletal muscle (muscle beta-spectrin) is present in two states, one associated with fodrin, and another that is not associated with any identifiable spectrin or fodrin subunit. Immunofluorescence studies indicate that a significant amount of beta-spectrin without alpha-fodrin is present in the myoplasm of some muscle fibers, and, more strikingly, at distinct regions of the sarcolemma. These results suggest that alpha-fodrin and muscle beta-spectrin associate in muscle in situ, but that some muscle beta-spectrin without a paired alpha-subunit forms distinct domains at the sarcolemma.