Two-variable nullcline analysis of ionic general equilibrium predicts calcium homeostasis in ventricular myocytes
Fig 5
Shocks in general equilibrium models. Change in SERCA uptake is a two-nullcline shock.
Panel (1): We show a hypothetical change in the cell that only affects one of the four surfaces. This produces a change in one of the nullclines. As an example, we pick an increase of the ΔQup surface. This leads to a shift of the g-nullcline to the right compared with the previous case, resulting in a lower diastolic level in the cytosol but larger in the SR. Panel (2): Effect of changing the maximum uptake of the SERCA pump from 0.15 μ M/ms to 0.3 μ M/ms in our rabbit model. Increasing the function of SERCA does not only affect the g-nullcline, expected since the uptake is larger, but also affects how well the exchanger works shifting also the f-nullcline to the right. The end result is similar to the previous case.