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Contractions of glycerinated skeletal (striated) and vascular (smooth) muscles are similar in their calcium dependence but differ in their magnesium dependence. The threshold concentration of free Ca(++) for contraction of either muscle was 1.8 x 10(-7)M; maximum tension developed when the concentration of free Ca(++) was slightly greater than 10(-6)M. The Mg concentration required for contraction of smooth muscle was at least ten times as great as that for skeletal muscle.
Filo et al. (Fri,) studied this question.