Ryanodol action on calcium sparks in ventricular myocytes

The action of ryanodol on single cardiac ryanodine receptor (RyR2) channels in bilayers and local RyR2-mediated Ca2+ release events (Ca2+ sparks) in ventricular myocytes was defined. At the single-channel level, ryanodol intermittently modified single channels into a long-lived subconductance state with an average duration of 3.8 ± 0.2 s. Unlike ryanodine, ryanodol did not change the open probability (Po) of unmodified channels, and high concentrations did not promote full-channel closure. Ryanodol action was Po dependent with the KD varying roughly from 20 to 80 μM as Po changed from ∼0.2 to 1, respectively. Ryanodol preferentially bound during long channel openings. In intact and permeabilized rat myocytes, ryanodol evoked trains of sparks at active release sites resulting in a significant increase in overall spark frequency. Ryanodol did not increase the number of active release sites. Long-lived Ca2+ release events were observed but infrequently, and ryanodol action was readily reversed upon drug washout. We propose that ryanodol modifies a few channels during a Ca2+ spark. These modified channels mediate a sustained low-intensity Ca2+ release that repeatedly triggers sparks at the same release site. We conclude that ryanodol is an easily generated reversible probe that can be effectively used to explore RyR2-mediated Ca2+ release in cells.