Simvastatin activates single skeletal RyR1 channels but exerts more complex regulation of the cardiac RyR2 isoform.

Background And Purpose: Statins are amongst the most widely prescribed drugs for those at risk of cardiovascular disease, lowering cholesterol levels by inhibiting 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase. Although effective at preventing cardiovascular disease, statin use is associated with muscle weakness, myopathies and, occasionally, fatal rhabdomyolysis. As simvastatin, a commonly prescribed statin, promotes Ca release from sarcoplasmic reticulum (SR) vesicles, we investigated if simvastatin directly activates skeletal (RyR1) and cardiac (RyR2) ryanodine receptors.

Experimental Approach: RyR1 and RyR2 single-channel behaviour was investigated after incorporation of sheep cardiac or mouse skeletal SR into planar phospholipid bilayers under voltage-clamp conditions. LC-MS was used to monitor the kinetics of interconversion of simvastatin between hydroxy-acid and lactone forms during these experiments. Cardiac and skeletal myocytes were permeabilised to examine simvastatin modulation of SR Ca release.

Key Results: Hydroxy acid simvastatin (active at HMG-CoA reductase) significantly and reversibly increased RyR1 open probability (Po) and shifted the distribution of Ca spark frequency towards higher values in skeletal fibres. In contrast, simvastatin reduced RyR2 Po and shifted the distribution of spark frequency towards lower values in ventricular cardiomyocytes. The lactone pro-drug form of simvastatin (inactive at HMG-CoA reductase) also activated RyR1, suggesting that the HMG-CoA inhibitor pharmacophore was not responsible for RyR1 activation.

Conclusion And Implications: Simvastatin interacts with RyR1 to increase SR Ca release and thus may contribute to its reported adverse effects on skeletal muscle. The ability of low concentrations of simvastatin to reduce RyR2 Po may also protect against Ca -dependent arrhythmias and sudden cardiac death.