Figure 1. Single native RyR1 channels are activated by DIDS.

(A) Channel current traces of a single native RyR1 activated by various concentrations of DIDS (0, 1, 10, 50 or 100 μM) are shown. DIDS was added to the cis side to activate the channel in the presence of 10 μM free Ca²⁺. Single-channel currents are shown as downward deflections from the closed level (indicated by c). Channel activities were recorded at a holding potential of −30 mV. (B) The plot of P_o versus various concentrations of DIDS is shown. The numerals and denominators shown in the parentheses represent the number of channels showing a reversibility and the number of channels used for the experiments respectively. The activity was monitored for over 120 s in each condition. The average P_o obtained at 10 μM Ca²⁺ was 0.15±0.02, which increased to 0.19±0.04, 0.44±0.04, 0.65±0.03, 0.71±0.03, 0.78±0.04 and 0.88±0.05 after addition of 1, 10, 30, 50, 75 and 100 μM DIDS respectively. At 1, 10 and 30 μM DIDS, the average P_o fell to 0.17±0.02, 0.15±0.06 and 0.18±0.03 respectively, after washing out DIDS with the cis solution for 2 min (reversible). On the other hand, at 50, 75 and 100 μM DIDS, the average P_o became 0.55±0.08, 0.68±0.05 and 0.80±0.06 respectively, after the washing out (irreversible).