Author:

Abstract:

S107 enhances ryanodine receptor calcium-dependant inactivation without impairing sarcolemmal L-type calcium channels Matthew Amoni*,# *Division of Cardiothoracic Surgery, Groote Schuur Hospital and University of Cape Town, Observatory, South Africa. #Katholieke Universiteit Leuven, Leuven, Belgium Objective: This study investigated the effects of S107, a ryanodine receptor (RyR)-specific derivative of the RyR-stabilising drug JVT519, on RyR calcium-dependant inactivation (CDI) and sarcolemmal L-type calcium currents. Methods: Left ventricular cardiomyocytes were isolated for patch-clamp recordings from wild-type BL6 mice by enzymatic digestion. Cells were incubated in either 10μM S107 or vehicle for 2 hours. Using an equimolar Cl-, Na2+- and K+-free patch pipette solution, 4 experimental groups were created, by adding: 10mM BAPTA (a potent Ca2+ chelator that eliminates CDI), or vehicle for the vehicle-incubated cells; and 10μM S107 or S107+BAPTA for the S107-incubated cells, to the pipette solution. ICaL currents were recorded by a voltage clamp protocol consisting of a depolarising pre-pulse followed by 10mV steps from -30 to +30 with train conditioning prior to each step. Recordings were performed in Na2+- and K+-free Tyrode’s bath solution maintained at 37°C. Data was captured in Clampex v8 and analysed with Clamp"t software. The tau of current’s ascending limb, a surrogate marker of CDI, was calculated as the "rst tau of a bi-exponential "t. Results: S107 signi"cantly reduced ICaL tau (S107: 4.2 ± 0.4, n=16, p< /0.05 vs. control: 8.3 ± 0.3, n=11), and BAPTA signi"cantly increased ICaL tau (BAPTA: 13.8 ± 1.8, n=9, p< /0.001 vs. control). The S107 effect was abolished by co-treatment with BAPTA (S107+BAPTA: 10.3 ± 0.8, n=3, p< /0.05). There were no differences in peak amplitude among the groups. Conclusions:These preliminary results suggest that S107 may enhance CDI through the proposed prevention of diastolic Ca2+ leak from the RyR, without affecting sarcolemmal Ca2+ handling. These findings may have clinical applications, suggesting that S107 can be an effective antiarrhythmic agent that improves intracellular Ca2+-handling. It also has the benefit of specificity and not affecting sarcolemmal L-type channel function, a property essential to improving contractility in heart failure.