Fig. 3.

The CPC2 inhibits RyR2 channel activity. (a) Cs⁺ currents obtained in the absence and presence of increasing concentration of GST-CPC2. Downward deflections represent channel openings. Experiments were performed under symmetrical conditions (250 mM CsCl in both the cis and trans side and 7–10 μM Ca²⁺ in the cis side). Currents traces were obtained at a holding potential of −25 mV and filtered at 400 Hz. To the right of each trace, the open state is represented as a dashed line, and the solid line represents the closed state. Open probability (Po) of channel at each concentration is shown on the right. (b) The CPC2 decreases the open probability of RyR2. Shown is concentration-dependent inhibition of RyR2 open probability when GST-CPC2 (filled circles; n = 3) and GST-NPC2 (open triangles; n = 3) is added to the cis side. Experiments were performed as described in Materials and Methods. (c) Ca²⁺-dependent inhibition of RyR2 by CPC2. The CPC2 decreases the open probability of RyR2 in the presence of increasing Ca²⁺ concentration (n = 3). Experiments were also performed in the absence (open circles) or presence (filled circles) of 17 μg/ml of GST-CPC2 (IC₅₀) in the cis side before Ca²⁺ additions.