Abstract

RyR is an intracellular Ca2+ channel that also is gated by this ion. RyR1, the skeletal muscle isoform, is closed at submicromolar Ca2+ concentrations, maximally activated at ∼20-50 micromolar Ca2+, and begins to inactivate at ∼100 micromolar cytosolic Ca2+ concentrations. Mg2+, a divalent cation with a constant concentration in the cell, inhibits RyR1 at physiological (mM) concentrations. Functional studies using tritiated ryanodine binding of RyR1 under different conditions of Ca2+ and Mg2+ revealed a dominant effect of Mg2+ over a wide range of Ca2+ concentrations, and similar inhibiting effect of the two divalent cations at mM concentrations.

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