Fig. 4.
. Redox-potential-dependent changes in channel activity are maintained in the presence of 2 mM ATP. (A–C) Channels exposed to cytoplasmic solutions having a reducing redox potential (RP) of −220 mV (n = 16). (D–F) Channels exposed to cytoplasmic solutions having a more oxidised redox potential of −180 mV (n = 11). (A,D) Descending from the upper trace, the data show the initial unbuffered redox activity (UR) with 1.0 mM luminal Ca2+ and 2.0 mM Na2ATP 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 activity as the luminal [Ca2+] was increased stepwise to 0.5 mM, 1 mM and 1.5 mM. (B,E) Mean open probability (Po) determined (a) for initial activity with 1 mM luminal Ca2+, (b) after adding 2 mM Na2ATP, (c) after adding GSH∶GSSG buffers and (d) after lowering luminal [Ca2+] to 0.1 mM. (C,F) Mean data for Po after stepwise increases in luminal [Ca2+]. (G–L) Mean gating parameter values. (G,J) Mean open time (To); (H,K) mean closed time (Tc); (I,L) mean frequency of opening (Fo). The bar graphs show mean parameter values (a) for initial activity with 1 mM luminal Ca2+, (b) after adding 2 mM Na2ATP, (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+).