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Intensity fluctuations in a laser beam scattered by nonbeating isolated rat cardiac muscle varied directly with the calcium concentrations in the bathing fluid. The steady-state level of these fluctuations varied directly with calcium-dependent force suggesting that the intensity fluctuations reflect an interaction of calcium ions with the myofilaments. The demonstration that both a portion of resting force and the frequency of intensity fluctuations vary directly with calcium even in quiescent conditions indicates that some contractile activation is present in the resting muscle.
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Lappé et al. (1980) studied this question.
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