Figure 8.

Voltage dependence of measured STOCs and simulated STOCs. To record and measure STOCs at large negative potentials, E_K was set at −28 mV. (A, left) Traces exhibit STOCs recorded at different holding potentials (V_h). Vertical bar, 25 pA for the V_hs between –100 and –40 mV, and 50 pA for all others. (right) Simulated STOCs from 25 RYR2 puncta at the V_hs shown on the left. Note that the vertical bar in the left column also applies to all voltages on the right and represents 25 pA, but the horizontal time bar on the left does not apply to the results on the right (because the temporal spacing between simulated STOCs is arbitrary). (B) Averaged conductance of STOC (G_(STOC)) as a function of voltage derived from measured (left) and simulated (right) STOCs (n = 6 cells for both cases in B and C). (C) TTOD_STOC (closed and open squares for experimental and simulated data, respectively) and τ_decay (closed and open triangles) as a function of voltage. (D) Spatial organization of RYRs and BK channels in ASM cells. RYR1 and RYR2 clusters localize near the plasma membrane and functionally couple with approximately two to three BK channel clusters to generate STOCs. RYR3 clusters distribute near the nucleus and could activate targets to be determined. BK channels in the plasma membrane outside the Ca²⁺ spark microdomains could be activated by unknown Ca²⁺-permeable channels. SR, sarcoplasmic reticulum. Error bars represent means ± SEM.