Figure 3.

Native cardiac MG23 channels displayed distinct gating properties from RyR2. A, the left panel shows representative Ca²⁺ current fluctuations mediated by MG23, recorded at various holding potentials. The traces were chosen to show current amplitudes clearly. The right panel shows a current-voltage relationship for MG23 using Ca²⁺ as a permeant ion. Data are shown as the mean ± S.D. (n = 5). B, representative current fluctuations through both MG23 and RyR2 channel gating in the same bilayer under control conditions with Ca²⁺ as a permeant ion at a holding potential of 0 mV. Cytosolic free Ca²⁺ was 5 μm. MG23 (O_MG23), RyR2 (O_RyR2) open, RyR2 + MG23 (O_RyR2+MG23) open and closed (C) states are indicated. The addition of 1 mm BAPTA to the cis chamber lowers Ca²⁺ to <4 nm. This Ca²⁺ concentration was sub-activating for RyR2 but had no effect on MG23. C, the top panel shows representative Ca²⁺ current fluctuations mediated through RyR2 under control conditions with Ca²⁺ as the permeant ion. Cytosolic-free Ca²⁺ was 5 μm. The addition of 10 mm caffeine to the cis chamber resulted in activation of RyR2 as expected. The lower panel shows a scatter plot of RyR2-channel open probability under these conditions. Data are shown as the mean ± S.D.; n = 3. ** denotes a significant difference (p < 0.01) to control. D, the top panel shows representative Ca²⁺ current fluctuations mediated through MG23 under control conditions using Ca²⁺ as the permeant ion. Cytosolic free Ca²⁺ was 5 μm. The addition of 10 mm caffeine to the cis chamber had no effect on MG23 channel activity. The lower panel shows a scatter plot of mean average current mediated through MG23 under these conditions. Data are shown as the mean ± S.D.; n = 3.