Prediction of Twitch and High Frequency Local Calcium Dynamics in Mouse EDL Fibers at 15-35°C

Abstract

Sites of calcium release, uptake and action are highly organized and densely packed in skeletal muscle cells. This organization suggests an important role for the spatial distribution of organelles and calcium sensitive proteins in muscle function. The current measurement techniques are not able to measure cytosolic [Ca2+] with both high temporal and high spatial resolution. In addition, it is known that all processes are highly temperature dependent. Therefore, the model of Groenendaal et al. [1], that describes local calcium dynamics at physiological frequencies at 35°C, was extended with Q10 correction factors and calcium-fluorescent dye binding kinetics, to predict local calcium dynamics at 15-35°C.For model validation, simultaneously calcium fluorescent dye and force kinetic measurements were performed. Hereto, murine EDL muscles were isolated and mounted in the set up. Muscle length was adjusted to optimal resting length and stimulation voltage was adjusted to generate maximal force. Rhod-2 AM was loaded in whole muscle at 37°C for 30 minutes or until force was decreased with >25%. Muscles were stimulated at 15-35°C at frequencies between twitch and tetanus.A significant relation was found between the temperature and the fluorescence characteristics, e.g. decrease in decay time with increasing temperature (one-way ANOVA, p-value<0.05). Model simulations predicted a comparable range. In addition, simulations showed an approximately five-fold difference in calcium gradient throughout the sarcomere between 15 and 35°C.The validated model is now able 1. to explain calcium fluorescent dye measurements, 2. to translate data at unphysiological to physiological temperature and 3. to predict local calcium dynamics at low and high frequency stimulations at a wide temperature range.[1] Groenendaal et al. IET Systems Biology, in press.