Fig. 2.

Ryanodol action is dose and open probability dependent. a Sample single RyR2 recordings in the absence (control) and presence of different ryanodol concentrations. Openings are upward deflections from marked closed current level. Recordings here were made a 20 mV. b Ryanodol dose–response plot revealing an EC₅₀ of 46.4±6 μM. Points are means and SEM of three to eight determinations. c Histograms of the time spent in the ryanodol modified (top) or unmodified states (bottom). Lines are single exponential fits. d Ryanodol action at different RyR2 Po levels. Sample recordings at 20 mV from three different channels before (control) and after 40 μM ryanodol was added to the cytosolic solution. These channels were activated by cytosolic Ca²⁺ (1 or 10 μM) or caffeine. Records at left are time compressed to better show the ryanodol action. e Summary results from 14 different channels exploring the relationship between Po and ryanodol action. These data were obtained from RyR2 channels activated by cytosolic Ca²⁺ (1, 5, or 10 μM; circles), cytosolic ATP (0.5, 1, or 2 mM; triangles), or cytosolic caffeine (5 mM; squares) in the presence of 40 μM ryanodol. The Po was measured during the unmodified periods (i.e., with ryanodol present). The top panel shows ryanodol modification duration as a function of Po. The center panel shows how the percentage of time the channel spends in the ryanodol modified state (%MOD) varies with Po. The bottom panel shows how the ryanodol apparent K_D varies with Po. The K_D here was determined from ryanodol association and dissociation rates using Eq. 2. The dissociation and association rates were determined by fitting of ryanodol-modified and unmodified duration histograms (as illustrated by part c). Thick solid lines in the lower two panels are linear regressions. Dotted lines represent 95% confidence bands