Figure 6.

Number of charges moved through NSR ion channels during diastole. When K⁺ channels are present (first three cases), they mediate roughly the same amount of charge across the NSR membrane (red) with very similar steady-state NSR-cytosol membrane potentials (values shown above the bars). The DKO case varies significantly because it has no K⁺ channels and therefore must counter the influx of charge by driving the low concentration of Cl⁻ through NSR Cl⁻ channels (orange), which requires a much larger polarization across the NSR-cytosol membrane (Fig. 5, blue line). Because the need for countercurrent is roughly the same for each case, the percent of total diastolic countercurrent mediated by NSR channels can be compared across cases (right axis). To see this figure in color, go online.