Fig. 3.

Effect of cytoplasmic and luminal GSH∶GSSG redox buffers on the response of RyR2 channels to changes in luminal [Ca²⁺]. In this and subsequent figures, the redox potential (RP) in all luminal solutions was −180 mV, the cytoplasmic [Ca²⁺] was 1.0 µM, channel activity was recorded at +40 mV, channel opening is upwards and open probability (P_o) values for each recording are shown above the broken line. (A–C,G–I) Channels exposed to cytoplasmic solutions having a reducing redox potential of −220 mV (n = 10). (D–F,J–L), channels exposed to cytoplasmic solutions having a more oxidised redox potential of −180 mV (n = 15). (A,D) Descending from the upper trace, the data show initial unbuffered redox (UR) activity with 1.0 mM luminal Ca²⁺, activity after addition of GSH∶GSSG with 1.0 µM luminal Ca²⁺, activity after perfusion with 0.1 mM Ca²⁺ luminal solution and replacement of GSH∶GSSG, then activity when luminal [Ca²⁺] was increased stepwise to 0.5 mM, 1 mM and 1.5 mM. P_o values for each recording are shown. (B,E) Mean P_o determined (a) for initial activity with 1 mM luminal Ca²⁺ and then (b) after adding GSH∶GSSG buffers and (c) after lowering luminal [Ca²⁺] to 0.1 mM. (C,F) Mean P_o after stepwise increases in luminal [Ca²⁺] from 0.1 mM to 1.5 mM. (G–L) Mean gating parameter values. (G,J) Mean open time (T_o); (H,K) mean closed time, (T_c); (I,L) mean frequency of opening (F_o). The bar graphs show mean parameter values (a) for initial activity with 1 mM luminal Ca²⁺, (b) after adding GSH∶GSSG buffers and (c) after lowering luminal Ca²⁺ to 0.1 mM. The line graphs are plots of mean parameter values as a function of luminal [Ca²⁺]. Data are shown as the mean±s.e.m.; ^#P<0.05 (versus the preceding condition); *P<0.05 (versus the mean value with 0.1 mM Ca²⁺).