TABLE IV The RYR2 Inactivation... | Rockefeller University Press

TABLE IV

The RYR2 Inactivation Associated with Various Combinations of Functional States among Its Four Subunits

Subunit stoichiometry	i	Opening rate constant, R_O	Closing rate constant, R_C	Probability of stoichiometry P_S	Probability of stoichiometry given closed, P_SC	Probability of stoichiometry given open, P_SO
3I 1O	1	φ	θ	\(4P_{I}^{3}P_{O}\)	\(4P_{I}^{3}P_{O}{\times}N/(1{+}{\phi}/{\theta})\)	\(4P_{I}^{3}P_{O}{\times}M/(1{+}{\theta}/{\phi})\)
4I 0O	2	φ	λ	\(P_{I}^{4}\)	\(P_{I}^{4}{\times}N/(1{+}{\phi}/{\lambda})\)	\(P_{I}^{4}{\times}M/(1{+}{\lambda}/{\phi})\)
others	3	φ	0	\(1{-}{{\sum}_{i{=}1}^{2}}P_{S}\)	0	\(\left(1{-}{{\sum}_{i{=}1}^{2}}P_{S}\right){\times}M\)

Subunit stoichiometry	i	Opening rate constant, R_O	Closing rate constant, R_C	Probability of stoichiometry P_S	Probability of stoichiometry given closed, P_SC	Probability of stoichiometry given open, P_SO
3I 1O	1	φ	θ	\(4P_{I}^{3}P_{O}\)	\(4P_{I}^{3}P_{O}{\times}N/(1{+}{\phi}/{\theta})\)	\(4P_{I}^{3}P_{O}{\times}M/(1{+}{\theta}/{\phi})\)
4I 0O	2	φ	λ	\(P_{I}^{4}\)	\(P_{I}^{4}{\times}N/(1{+}{\phi}/{\lambda})\)	\(P_{I}^{4}{\times}M/(1{+}{\lambda}/{\phi})\)
others	3	φ	0	\(1{-}{{\sum}_{i{=}1}^{2}}P_{S}\)	0	\(\left(1{-}{{\sum}_{i{=}1}^{2}}P_{S}\right){\times}M\)

The kinetic scheme for channel gating is shown in Fig. 10 (scheme 3). States O and I depend on Ca²⁺ and Mg²⁺ binding to the I₂-site, which is described in Table II B. Three inactivated subunits are needed to permit channel inactivation. Associated with each stoichiometry is the channel opening and closing rate constants, the probability that the channel has that stoichiometry, and the probabilities of the channel open and closed states. Values for the rate constants are given in Table V. The values M and N are normalizing factors:

\[N{=}1\left/{{\sum}_{i{=}1}^{3}}P_{SCi}\right.,\]

\[M{=}1\left/{{\sum}_{i{=}1}^{3}}P_{SOi}\right..\]

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