Figure 6.

Functional effect of HdCa (hadrucalcin) on single RyR1 (ryanodine receptor, skeletal isoform) activity. Heavy sarcoplasmic reticulum vesicles from skeletal muscle were fused to lipid bilayers as described in Methods, and the activity of single RyRs was elicited by adding 10 µmol·L⁻¹ Ca²⁺ to the cis (cytosolic) side of the channel. Upper panel: left, activity of a single RyR in the absence of HdCa (control) and its corresponding current histogram (right). The closed state of the channel corresponds to 0 pA. Bottom panel: the same channel immediately after perfusion of a 2 µL solution containing HdCa (30 nmol·L⁻¹ final) into the cis side of the channel. The current histogram shows a prominent peak centred at 10 pA, which corresponds to the amplitude of the subconductance state induced by HdCa (arrows). Holding potential was 30 mV for all recordings, and openings are represented by upward deflections of the baseline current. Experiment is representative of four independent experiments.