Temperature dependence and thermodynamic properties of Ca2+ sparks in rat cardiomyocytes.
To elucidate the temperature dependence and underlying thermodynamic determinants of the elementary Ca2+ release from the sarcoplasmic reticulum, we characterized Ca2+ 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 Ca2+ sparks decreased monotonically, but the Delta[Ca2+]i were relatively unchanged due to increased resting [Ca2+]i. The time-to-peak of Ca2+ sparks, which represents the RyR Ca2+ 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 Ca2+ concentration. These results provided a basis for quantitative interpretation of intracellular Ca2+ signaling under various thermal conditions. The relative temperature insensitivity above the transitional 25 degrees C led to the notion that Ca2+ sparks measured at a "warm room" temperature are basically acceptable in elucidating mammalian heart function.
Fu
Yu
Y
National Key Laboratory of Biomembrane and Membrane Biotechnology, College of Life Sciences, Peking University, Beijing 100871, China.
Zhang
Guang-Qin
GQ
Hao
Xue-Mei
XM
Wu
Cai-Hong
CH
Chai
Zhen
Z
Wang
Shi-Qiang
SQ
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D002478:Cells, Cultured; D003198:Computer Simulation; D007700:Kinetics; D008954:Models, Biological; D032383:Myocytes, Cardiac / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D013696:Temperature; D013816:Thermodynamics
D019837:Ryanodine Receptor Calcium Release Channel; D002118:Calcium