Effects of HMG-CoA reductase inhibitors on excitation-contraction coupling of rat skeletal muscle.

3-Hydroxy-3-methyl glutaryl coenzyme A (HMG-CoA) reductase inhibitors currently used as cholesterol-lowering drugs produce side effects in patients, one of which is myopathy. In the present study we compared the effect of a 3-month chronic treatment with two different compounds, simvastatin and pravastatin, on the excitation-contraction coupling of rat skeletal muscle fibers, the mechanism which links membrane depolarization to the movements of cytosolic Ca2+ from intracellular stores. The voltage threshold for mechanical activation of extensor digitorum longus muscle fibers in response to depolarizing pulses of various durations was studied in vitro by the two intracellular microelectrode method in 'point' voltage clamp mode. Simvastatin (5-50 mg/kg) modified the mechanical threshold of striated fibers in a dose-dependent manner. The muscle fibers of rats treated with 10 mg/kg and 50 mg/kg of simvastatin needed significantly less depolarization to contract than did untreated fibers at each pulse duration, suggesting that levels of cytosolic Ca2+ were higher. Consequently, the rheobase voltage for fiber contraction was significantly shifted toward more negative potentials with respect to controls by 2.4 mV and 7.1 mV in the 10 mg/kg and 50 mg/kg simvastatin-treated animals, respectively. Pravastatin treatment at 100 mg/kg did not produce any alteration of excitation-contraction coupling since the rheobase voltage was similar to that of controls. The different physicochemical properties of the two drugs may underlie the different effect observed because lipophilic agents, such as simvastatin, have been shown to affect sterol biosynthesis in many tissues, whereas the hydrophilic pravastatin is hepato-selective.