Control of heat production by the Ca21-ATPase of rabbit and trout sarcoplasmic reticulum

De Meis, Leopoldo. Control of heat production by the Ca21-ATPase of rabbit and trout sarcoplasmic reticulum. Am. J. Physiol. 274 (Cell Physiol. 43): C1738–C1744, 1998.—The sarcoplasmic reticulum Ca21-ATPase of rabbit skeletal muscle can convert the energy derived from a Ca21 gradient into heat (L. de Meis, M. L. Bianconi, and V. A. Suzano. FEBS Lett. 406: 201–204, 1997). In this report, it is shown that this conversion varies depending on the temperature and on whether rabbit (endotherm) or trout (poikilotherm) sarcoplasmic reticulum vesicles are used. The gradient doubled the yield of heat produced during ATP hydrolysis and the calorimetric enthalpy of ATP hydrolysis (DHcal) value found with both rabbit and trout varied between 210 and 212 kcal/mol in leaky vesicles (no gradient) and between 220 and 222 kcal/mol with intact vesicles (gradient). For the rabbit, the difference of DHcal measured with and without gradient was detected in the range of 30–35°C and disappeared when the temperature was decreased below 30°C. For the trout, the difference was detected between 20 and 25°C and disappeared below 20°C. The effect of the gradient on the DHcal for ATP hydrolysis was modified by DMSO, trifluoperazine, and heparin sodium.