The interactions between membrane enzymes and membrane lipids are sensitive to a shift in temperature that causes changes of the membrane structure. Temperature dependence of membrane bound enzymes usually displays a break in the Arrhenius plot. In this study we used Ca²⁺-ATPase from the sarcoplasmic reticulum (SERCA) derived from skeletal muscle. In order to compare endothermic (constant body temperature) and exothermic (body temperature varies with environment) animals, we used rabbit and goldfish.

            Goldfish were acclimated at 5º and 25ºC during one week (cold- and warm-acclimation, respectively). Vesicles derived from the sarcoplasmic reticulum of goldfish and rabbit muscles were prepared and Ca²⁺-ATPase activity of the three preparations was measured in temperatures varying between 5º and 45ºC. Both warm- and cold-acclimated goldfish presented the same temperature dependence. The rates of Ca²⁺ uptake and Ca²⁺-ATPase activity increased progressively from 5º up to 40ºC and at 45º either decreased or remained at the same value as that measured at 40º.  In range of 5-40ºC vesicles derived from rabbit muscle displayed the same temperature dependence as that of goldfish. Raising the temperature from 40º to 45º however, promoted a further increase of the rabbit Ca²⁺ ATPase.

            These results indicated that the acclimation process of goldfish does not involve a significant change of the Ca²⁺-ATPase thermal dependence.  In the range of 5º to 40º there was also no variation between endothermic (rabbit) and exothermic (goldfish) animals.