Characterization of Ca2+- and Sr2+-activated tension in functionally skinned chicken fibers of normal and dystrophic skeletal and normal cardiac muscle

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Abstract
The Ca2+ and Sr2+ activation of tension in functionally skinned chicken fibers of normal and dystrophic skeletal and normal cardiac muscle were studied. The muscles studied can be separated into two groups based upon their Ca2+ and Sr2+ sensitivities: those which are significantly more sensitive to Ca2+ than to Sr2+, pectoralis and posterior latissimus dorsi (PLD), and those which show no Ca2+/Sr2+ sensitivity difference, cardiac and anterior latissimus dorsi (ALD). This suggests that there is more than one type of Ca2+ site involved in Ca2+ control of muscle contraction in different muscle types and suggests that ALD and cardiac muscle may be controlled by a different type of binding site than PLD and pectoralis muscle. Dystrophic ALD and PLD muscles showed little change in their Ca2+ and Sr2+ sensitivities from those of normal muscles in contrast to the pectoralis which showed a decrease in both Ca2+ and Sr2+ sensitivity (approaching that of PLD) with the onset of dystrophy. Similarly, upon SDS polyacrylamide gel electrophoresis, dystrophic ALD and PLD muscles showed no difference in contractile proteins from those of normal muscles, in contrast to pectoralis muscle where the appearance of a 36,000 dalton protein band correlated with the onset of dystrophy and the changes in the Ca2+/Sr2+ activation properties of this muscle. The contractile protein band pattern of normal and dystrophic PLD and dystrophic pectoralis muscle were similar including the presence of the 36,000 dalton protein.