Аннотация
To elucidate the temperature dependence and underlying thermodynamic
determinants of the elementary Ca$^2+$ release from the sarcoplasmic
reticulum, we characterized Ca$^2+$ sparks originating from ryanodine
receptors (RyRs) in rat cardiomyocytes over a wide range of temperature.
From 35 degrees C to 10 degrees C, the normalized fluo-3 fluorescence
of Ca$^2+$ sparks decreased monotonically, but the DeltaCa$^2+$(i)
were relatively unchanged due to increased resting Ca$^2+$(i).
The time-to-peak of Ca$^2+$ sparks, which represents the RyR
Ca$^2+$ release duration, was prolonged by 37\% from 35 degrees
C to 10 degrees C. An Arrhenius plot of the data identified a jump
of apparent activation energy from 5.2 to 14.6 kJ/mol at 24.8 degrees
C, which presumably reflects a transition of sarcoplasmic reticulum
lipids. Thermodynamic analysis of the decay kinetics showed that
active transport plays little role in early recovery but a significant
role in late recovery of local Ca$^2+$ concentration. These results
provided a basis for quantitative interpretation of intracellular
Ca$^2+$ signaling under various thermal conditions. The relative
temperature insensitivity above the transitional 25 degrees C led
to the notion that Ca$^2+$ sparks measured at a "warm room" temperature
are basically acceptable in elucidating mammalian heart function.
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