Fig. 4.

Quantitative hypotheses testing; experimental data vs. model simulations. Experimental data are indicated in black. Error bars indicate SE (n = 4–5). Simulation results according to model configuration i (without calcium activation of PFK-1, red lines) and model configuration ii and iii (with calcium activation of PFK-1, green and blue, respectively) are shown. Optimized model parameter values listed in Table 3 were obtained by fitting model stimulations to these data. A–E: PCr. F–J: pH. K–O: predictions according to model configuration iii (solid lines) of ATP supply flux by PCr hydrolysis (grey lines) and glycolysis (black lines) and ATP demand flux (blue lines), compared with values derived from the experimental data by using the phenomenological model (dots) described by Conley et al. (9). Calculations with the phenomenological model were performed using the estimated value of the static proton buffer capacity as listed in Table 3. As a result of the fast (de)activation kinetics of PFK-1 (see Fig. 7) the net glycolytic ATP synthesis flux was also pulsatile. For clarity of presentation, the glycolytic flux (black lines) indicated represents the net flux averaged over epochs of 5 s.