"Slow" myosins in vertebrae skeletal muscle. An immunofluorescence study.

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Abstract
Specific antisera were raised in rabbits against column-purified myosins from a slow avian muscle, the chicken anterior latissimus dorsi (ALD), and a slow-twitch mammalian muscle, the guinea pig soleus (SOL). The antisera were labeled with fluorescein and applied to sections of muscles from various vertebrate species. Two distinct categories of the slow fibers were identified on the basis of their differential reactivity with the 2 antisera. Fibers stained by anti-ALD appear to correspond in distribution and histochemical properties to physiologically slow-tonic fibers, i.e., fibers that display multiple innervation and respond to stimulation with prolonged contractures. In mammals, only a minority of fibers in extraocular muscles and the nuclear bag fibers of muscle spindles were brightly labeled by this antiserum. Fibers labeled by anti-SOL in mammalian muscle appear to correspond in distribution and histochemical properties to physiologically slow-twitch fibers. Anti-SOL stained a population of fibers in reptiles, amphibians and fishes that did not react, or reacted poorly, with anti-ALD; in avian muscle, only a minor proportion of the slow fibers were labeled by anti-SOL. Two antigenically distinct, though partly cross-reacting, types of slow myosin in vertebrate muscle exist.