Fig. 5.

Flecainide and tetracaine block single RyR2 channels by different mechanisms.

(A,B) Records are representative examples of single channel activity of RyR2 in lipid bilayers. Control conditions were 1 mM luminal Ca²⁺ (trans bath), 0.1 μM cytoplasmc Ca²⁺ plus 2 mM ATP (cis bath). Bilayer potential was 40 mV (relative to trans bath as ground). Relatively high concentrations of flecainide (FLEC) and tetracaine (TET) were used to better illustrate their differential effect on RyR2 channel gating.

(A) Single experiment where flecainide was added to the cytoplasmic bath. Under control conditions, this channel had an open probability (P_o) of 0.25, mean open time (τ_o) of 83 ms and mean closed time (τ_c) of 228 ms. The full duration of typical closed periods is not seen on this time scale. Addition of flecainide introduced short (∼ 1 ms) closures to a substate at ∼20% of the full channel conductance which lead to bursts of short channel openings.

(B) Different experiment where tetracaine was added to the bath. Under control conditions, this channel had P_o = 0.11, τ_o = 33 ms and τ_c = 237 ms. Addition of 100 μM tetracaine increased τ_c to 913 ms but had little effect on τ_o (τ_o =27 ms).

(C) The effects of flecainide and tetracaine on burst parameters were compared at concentrations that reduced RyR2 Po by approximately 50% (10 μM and 50 μM, respectively).

(D-F) Comparison of average burst parameters derived from burst analyses of single channel recordings. The data are expressed as burst properties relative to control before addition of FLEC or TET (control conditions are given in methods). Note that FLEC inhibits RyR2 by reducing burst duration (D) and intraburst Po (E), whereas TET increased the interburst closed duration (F). *p<0.05, **p<0.01, n=10 per group