The structure of the longitudinal body muscles of Branchiostoma caribaeum has been studied by light and electron microscopy. These muscles are shown to be composed of fibers in the form of flat lamellae about 0.8µ in thickness, more than 100 µ wide, and reaching in length from one intermuscular septum to the next, a distance of about 0.6 mm. Each flat fiber is covered by a plasma membrane and contains a single myofibril consisting of myofilaments packed in the interdigitating hexagonal array characteristic of vertebrate striated muscle. Little or no sarcoplasmic reticulum is present. Mitochondria are found infrequently and have a tubular internal structure. These morphological observations are discussed in relation to a proposed hypothesis of excitation-contraction coupling. It is pointed out that the maximum distance from surface to myofilament in these muscles is about 0.5 µ and that diffusion of an "activating" substance over this distance would essentially be complete in less than 0.5 msec. after its release from the plasma membrane. It is concluded that the flat form of amphioxus muscle substitutes for the specialized mechanisms of excitation-contraction coupling thought possibly to involve the sarcoplasmic reticulum in higher vertebrate muscles.
Article| August 01 1961
STRUCTURE OF THE LONGITUDINAL BODY MUSCLES OF AMPHIOXUS
Lee D. Peachey
From The Rockefeller Institute.
Dr. Peachey's present address is Department of Zoology, Columbia University, New York
Received: May 31 1960
Copyright, 1961, by The Rockefeller Institute Press
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Lee D. Peachey; STRUCTURE OF THE LONGITUDINAL BODY MUSCLES OF AMPHIOXUS . J Biophys and Biochem Cytol 1 August 1961; 10 (4): 159–176. doi: https://doi.org/10.1083/jcb.10.4.159
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