Fig. 5.

. Redox-potential-dependent changes in channel activity are maintained in the presence of 1 mM free Mg²⁺. (A–C) Channels exposed to cytoplasmic solutions with reducing redox potential (RP) of −220 mV (n = 8). (D–F) Channels exposed to cytoplasmic solutions with a more oxidised redox potential of −180 mV (n = 8). (A,D) Descending from the upper trace, the data show the initial unbuffered redox activity (UR) with 1.0 mM luminal Ca²⁺ and 5.0 mM MgATP in the cytoplasmic solution, the activity after addition of GSH∶GSSG buffers with 1.0 µM luminal Ca²⁺, the activity after perfusion with 0.1 mM Ca²⁺ luminal solution and replacement of GSH∶GSSG, and then the activity as luminal [Ca²⁺] was increased stepwise to 0.5 mM, 1 mM, and 1.5 mM. (B,E) Mean open probability (P_o) determined (a) for initial activity with 1 mM luminal Ca²⁺, (b) adding 5.0 mM MgATP, (c) after adding GSH∶GSSG buffers and (d) after lowering luminal Ca²⁺ to 0.1 mM. (C,F) Mean data for P_o after stepwise increases in luminal [Ca²⁺]. (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 5.0 mM MgATP, (c) after adding GSH∶GSSG buffers and (d) 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⁺).