FIGURE 8.

Single chimeric N-RyR1/C-RyR2 and N-RyR2/C-RyR1 channels exhibit different responses to luminal Ca²⁺. Single-channel activities of N-RyR1/C-RyR2 (A) and N-RyR2/C-RyR1 (B) were recorded in a symmetrical recording solution containing 250 mM KCl and 25 mM Hepes (pH 7.4), as described in the legend to Fig. 3. (A) The control current traces for N-RyR1/C-RyR2 at 310 nM cytoplasmic Ca²⁺ are shown in a and single-channel current traces at 45 nM (b), 2 μM (c), 100 μM (d), 600 μM (e), 2.5 mM (f), and 5 mM (g) luminal Ca²⁺ are also depicted. (B) The control current traces for N-RyR2/C-RyR1 are shown in a and single-channel current traces at 45 nM (b), 2.5 mM (c), 5 mM (d), 10 mM (e), 20 mM (f), and 40 mM (g) luminal Ca²⁺ are also shown. The holding potential was −20 mV. Openings are downward. Open probability (P_o), arithmetic mean open time (T_o), and arithmetic mean closed time (T_c) are indicated on the top of traces. A short line to the right of each current trace indicates the baseline. The relationships between P_o and luminal Ca²⁺ concentrations of single N-RyR1/C-RyR2 (A h) and N-RyR2/C-RyR1 (B h) channels are shown in comparison with those of single RyR2 and RyR1 channels, respectively. Data points shown are mean ± SE from six single N-RyR1/C-RyR2 and five single N-RyR2/C-RyR1 channels.