Atorvastatin Activates Skeletal Ryr1 Channels: Towards Reducing Statin Side-Effects

We have previously reported that simvastatin can activate single skeletal muscle ryanodine receptor (RyR1) channels gating in artificial membranes and stimulate sarcoplasmic reticulum (SR) Ca2+ release from isolated skeletal muscle cells. We suggested that the interaction of statins with RyR1 may contribute to their muscle-related side effects, including fatal rhabdomyolosis. We therefore investigated whether RyR1 channel activation is a common property of clinically relevant statins, focusing on atorvastatin, a more recently developed and fully synthetic drug. Sheep skeletal RyR1 were incorporated into planar phospholipid bilayers under voltage-clamp conditions as previously described (Sitsapesan et al., 1991, J Physiol., 434:469-488). Low concentrations of cytosolic atorvastatin significantly increased Po from 0.029±0.0098 (mean±SEM, n=12) in control conditions to 0.077±0.023 (mean±SEM, n=12, p<0.05) with 100 nM atorvastatin and 0.083±0.027 (SEM, n=11, P<0.05) with 1µM atorvastatin. Atorvastatin appears to sensitise RyR1 channels to the effects of cytosolic Ca2+ since it was unable to activate RyR1 at sub-activating cytosolic [Ca2+]. The addition of atorvastatin to the luminal side of RyR1 did not activate the channels even at high concentrations (≤100 µM), indicating that atorvastatin does not cross the bilayer and that it interacts with RyR1 via cytosolic binding sites. Atorvastatin also significantly increased [3H]ryanodine binding to sheep skeletal SR membranes, which further demonstrates its potential to promote RyR1 channel opening. As a means of developing a statin with fewer side effects, we now aim to utilise a medicinal chemistry approach to design an effective 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor that can lower blood cholesterol levels yet does not activate RyR1. Funded by the BHF Centre of Research Excellence, Oxford