Control of heat production by the Ca2+-ATPase of rabbit and trout sarcoplasmic reticulum

The sarcoplasmic reticulum Ca2+-ATPase of rabbit skeletal muscle can convert the energy derived from a Ca2+ gradient into heat (L. de Meis, M. L. Bianconi, and V. A. Suzano. FEES 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)sa ulum vesicles are used. The gradient doubled the yield of heat produced during ATP hydrolysis and the calorimetric enthalpy of ATP hydrolysis (Delta H-cal) value found with both rabbit and trout varied between -10 and -12 kcal/mol in leaky vesicles (no gradient) and between -20 and -22 kcal/mol with intact vesicles (gradient). For the rabbit, the difference of Delta H-cal measured viith and without gradient was detected in the range of 30-35 degrees C and disappeared when the temperature was decreased below 30 degrees C. For the trout, the difference was detected between 20 and 25 degrees C and disappeared below 20 degrees C. The effect of the gradient on the Delta H-cal for ATP hydrolysis was modified by DMSO, trifluoperazine, and heparin sodium.