The Ca2+ Permeation Mechanism of the Ryanodine Receptor Revealed by a Multi-Site Ion Model

The ryanodine receptors (RyR) are ion channels responsible for the release of Ca2+ from the sarco/endoplasmic reticulum and play a crucial role in the precise control of Ca2+ concentration in the cytosol. The detailed permeation mechanism of Ca2+ through RyR is still elusive. By using molecular dynamics simulations with a specially designed Ca2+ model, here we show that multiple Ca2+ accumulate in the upper selectivity filter of RyR1, but only one Ca2+ can enter and translocate in the narrow pore at a time. The Ca2+ is nearly fully hydrated during the whole permeation process, with the first solvation shell intact even at the narrowest constrict sites of the selectivity filter and gate. These results present a one-at-a-time permeation pattern for the hydrated ions, which is distinct from the fully/partially dehydrated knock-on permeation in K+ and Na+ channels and uncovers the underlying reason for the high permeability and low selectivity of the RyR channels.