Figure 6. Inhibitory effect of cytosolic Mg2+ on the activity of the ATP-activated RYR2 channel. (A) Representative current traces of single RYR2 channels recorded at 0.5 (top), 1 (middle) and 8 mM [Ca2+]L (bottom) at free [Mg2+]C spanning the whole inhibitory range (0–0.39, 0–0.39, and 0–0.55 mM, respectively). All channels were activated by 10 mM ATP at 410 nM [Ca2+]C to reach the maximal level of channel activation. Channel openings are in the upward direction. Dashes at the left of the traces indicate the closed state of the channel. (B) The free [Mg2+]C dependence of normalized RYR2 PO in the presence of 0.5, 1, 8, and 53 mM [Ca2+]L (open squares and circles, and black triangles and diamonds, respectively). Solid lines are Hill equation fits obtained by fitting the whole dataset at 0.5–53 mM [Ca2+]L simultaneously when nH and IC50 as fitted parameters were shared.
Figure 6.

Inhibitory effect of cytosolic Mg2+ on the activity of the ATP-activated RYR2 channel. (A) Representative current traces of single RYR2 channels recorded at 0.5 (top), 1 (middle) and 8 mM [Ca2+]L (bottom) at free [Mg2+]C spanning the whole inhibitory range (0–0.39, 0–0.39, and 0–0.55 mM, respectively). All channels were activated by 10 mM ATP at 410 nM [Ca2+]C to reach the maximal level of channel activation. Channel openings are in the upward direction. Dashes at the left of the traces indicate the closed state of the channel. (B) The free [Mg2+]C dependence of normalized RYR2 PO in the presence of 0.5, 1, 8, and 53 mM [Ca2+]L (open squares and circles, and black triangles and diamonds, respectively). Solid lines are Hill equation fits obtained by fitting the whole dataset at 0.5–53 mM [Ca2+]L simultaneously when nH and IC50 as fitted parameters were shared.

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