Effect Of Simvastatin On The Caffeine-and Halothane-induced Calcium Release Reaction In Skeletal Muscle

Introduction:Statins,the cholesterol lowering HMG-CoA reductase inhibitors,are widely used for their benefits of lowering the risk of cardiovascular incidence.Even though they are generally well tolerated,various forms of skeletal muscle toxicity (ranging from transient increase in creatine kinase to life-threatening rhabdomyolysis) occur frequently.Individuals with statins-induced myotoxic symptoms may show a positive caffeine-halothane contracture test(CHCT) result,an indication of malignant hyperthermia susceptible(MHS),which may put them at potential risks during surgery and anesthesia.On the other hand,some patients with atypical presentation of malignant hyperthermia(such as increase in creatine kinase or rhabdomyolysis without hyperthermia) also had a statins-administration history.Objective:The purpose of this study was to determine whether the myotoxic side effect of simvastatin,a typical statins,might influence skeletal muscle's susceptibility to caffeine and halothane.Methods:Primary cultured neonate rat skeletal myotubes were treated with 0.01～5μM simvastatin for 48 hours.MTT was used to evaluate myotubes viability.The gross morphology and microstructure of the myotubes were observed with light microscope and electronmicroscope respectively.Quantitative immuno-fluorescence was used to measure the expression of ryanodine receptors type 1(RyR1),a calcium release channel in the sarcoplasmic reticulum(SR) membrane.The intracellular calcium concentration ([Ca²⁺]i) at rest and in response to depolarization(with 60mM KC1) and caffeine and halothane were investigated by fluorescence calcium imaging.Data was analyzed by ANOVA test.Results were shown as mean±SD and difference was considered significant at P＜0.05.Result:Simvastatin(0.01～5μM) dose-dependently depressed the myotubes viability, changed the morphological features and microstructure,inhibited the expression of RyR1 and increased the resting[Ca²⁺]i.Compared with the control group,the SR calcium content increased to the peak level in myotubes treated with 0.01μM simvastatin, and then fell back or even decreased in myotubes treated with higher dose(0.1～5μM) of simvastatin.Simvastatin(0.01～5μM) did not change myotubes sensitivity to low-dose caffeine(0.625～2.5mM) and halothane(1～10mM)(P＞0.05).While,in response to 60mM KC1 and high-dose caffeine(10mM and 20mM) and halothane(20Mm and 40mM),myotubes treated with 0.01μM simvastatin showed a significant increased sensitivity(P＜0.05);the sensitivity of myotubes treated with 0.1μM simvastatin did not changed significantly(P＞0.05);myotubes treated with 1μM and 5μM simvastatin showed a significant decreased sensitivity(P＜0.05).Conclusion:The myotoxic side effect of simvastatin may change myotubes sensitivity to high-dose caffeine and halothane.The sensitivity may be increased when the toxicity is weak and the myotubes are still at the stage of self-compensation;but may be decreased when the toxicity is strong and the myotubes are at stage of decompensation with internal structure and functional damage.