In this work, the temperature dependence of the sarco–endoplasmic reticulum Ca2+‐ATPase (SERCA2) activity from rainbow trout Oncorhynchus mykiss cardiac ventricles was measured and compared with the mammalian SERCA2 isoform. The rate of ATP‐dependent
Ca2+ transport catalysed by O. mykiss vesicles was totally abolished by thapsigargin and the Ca2+ ionophore A23187. At warm temperatures (25 and 30° C), the SERCA2 from O. mykiss ventricles displayed the same rate of Ca2+ uptake.
At 35° C, the activity of the O. mykiss enzyme decreased after 20 min of reaction time. The rate of Ca2+ uptake catalysed by the mammalian SERCA2 was temperature dependent exhibiting its maximal activity at 35° C. In contrast to the rate of Ca2+ uptake,
the rate of ATP hydrolysis catalysed by O. mykiss SERCA2 was not significantly different at 25 and 35° C, but the rate of ATP hydrolysis catalysed by the rat Rattus norvegicus SERCA2 isoform at 35° C was two‐fold higher than at 25° C. At low temperatures (5
to 20° C), the rate of Ca2+ uptake from O. mykiss SR was less temperature dependent than the R. norvegicus isoform, being able to sustain a high activity even at 5° C. The mean ±s.e. Q10 values calculated from 25
to 35° C for ATP hydrolysis were 1·112 ± 0·026 (n = 3) and 2·759 ± 0·240 (n = 5) for O. mykiss and R. norvegicus, respectively. Taken together, the results show that the O. mykiss SERCA2 was not temperature dependent
over the 10 to 25° C temperature interval commonly experienced by the animal in vivo. The Q10 value of SERCA2 was significantly lower in O. mykiss than R. norvegicus which may be key for cardiac function over the wide environmental temperatures experienced
in this eurythermal fish.