Relationship of mitochondria and sarcoplasmic reticulum to cold shortening.

Sarcoplasmic reticulum and mitochondria preparations from beef and rabbit muscle were shown to bind and release appreciable quantities of Ca(++). Differences between rabbit and beef muscle in Ca(++) binding and release by SR and mitochondrial preparations were not sufficient to account for the massive shortening in chilled beef as compared to little or no shortening in chilled rabbit muscle. Results substantiate the theory of Buege & Marsh (1975) that cold shortening is related to differences in mitochondrial concentration in red and white muscle rather than to differences in the Ca(++)-accumulating ability of SR. In order to explain the reversibility of cold shortening upon rewarming pre-rigor red muscle, a role for both SR and mitochondria is postulated and discussed.