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Subunit structure of junctional feet in triads of skeletal muscle: A freeze-drying rotary-shadowing study

By Donald G. Ferguson, Harry W. Schwartz and Clara Franzini- Armstrong

Abstract

ABSTRACT Isolated heavy sarcoplasmic reticulum vesicles retain junctional specializations (feet) on their outer surface. We have obtained en face three-dimensional views of the feet by shadowing and replicating the surfaces of freeze-dried isolated vesicles. Feet are clearly visible as large structures located on raised platforms. New details of foot structure include a four subunit structure and the fact that adjacent feet do not abut directly corner to corner but are offset by half a subunit. Feet aligned within rows were observed to be rotated at a slight angle off the long axis of the row creating a center-to-center spacing (32.5 nm) slightly less than the average diagonal of the feet (35.3 nm). Comparison with previous information from thin sections and freeze-fracture showed that this approach to the study of membranes faithfully preserves structure and allows better visualization of surface details than either thinsectioning or negative-staining. Downloaded from jcb.rupress.org The triads of vertebrate skeletal muscles are specialized junctions formed by the interposition of a T tubule between two terminal cisternae of the sarcoplasmic reticulum (SR)? I

Year: 1984
OAI identifier: oai:CiteSeerX.psu:10.1.1.318.7056
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