Cold‐contracture and atp‐turnover in the red and white musculature of the pig, post mortem

Cold‐contracture at 2°C has been studied in some 8 multitoned muscles in the hind limb of the pig, in relation to the myoglobin content. Maximal myo‐fibrillar ATPase activity has also been measured, as a guide to muscle speed. Contracture occurs in two phases, the first phase being highly pH and load‐dependent. The latter is much restricted in extent below pH 6.7. Second phase contracture is akin to rigor contracture at higher temperatures; it can be extensive in some muscles, such as LD and SM(W) which often have initial pH values too low for phase 1 contracture to occur. Phase 1 contracture is highly correlated with the myoglobin content whereas muscle speed is inversely related to it. In these pig muscles, therefore, the fast/white, slow/red rule applies in all cases except the LD, which is white and fast, but cold‐contracts as vigorously as the red muscles. An explanation of this anomaly is put forward in terms of the actomyosin ATPase, turned on by the postulated release of Ca2+ at temperatures below 15°C.