Figure 1. Structure of the model. The... | Rockefeller University Press

Figure 1.

$Figure 1. Structure of the model. The model consists of 10,000 independent couplons, each with a dense square cluster of RyRs in a dyadic cleft, with an associated JSR release terminal. The JSR is refilled by intra-lumenal diffusion from calcium in the FSR (SR uptake compartment), which is assumed to be an infinite compartment at resting calcium CaSR0 because isolated sparks are being considered. Two models of the refilling connection were considered. In the simplest (A), the JSR refills through a single diffusional resistance, characterized by the refilling rate constant Dup. As discussed in the Results, it is difficult to reconcile the observed refilling rate with simple diffusion theory. We therefore constructed a second version of the model (B) in which the connection is made through a tube of local FSR, whose length and diameter are chosen to match the observed steady-state diffusion resistance (characterized by time constant τfill) and the observed volume fraction of FSR. For the standard parameters and a true half-sarcomere length of 1 µm, the effective SR tube length is 1.995 µm.$

Structure of the model. The model consists of 10,000 independent couplons, each with a dense square cluster of RyRs in a dyadic cleft, with an associated JSR release terminal. The JSR is refilled by intra-lumenal diffusion from calcium in the FSR (SR uptake compartment), which is assumed to be an infinite compartment at resting calcium CaSR₀ because isolated sparks are being considered. Two models of the refilling connection were considered. In the simplest (A), the JSR refills through a single diffusional resistance, characterized by the refilling rate constant D_up. As discussed in the Results, it is difficult to reconcile the observed refilling rate with simple diffusion theory. We therefore constructed a second version of the model (B) in which the connection is made through a tube of local FSR, whose length and diameter are chosen to match the observed steady-state diffusion resistance (characterized by time constant τ_fill) and the observed volume fraction of FSR. For the standard parameters and a true half-sarcomere length of 1 µm, the effective SR tube length is 1.995 µm.