Establishment of a human skeletal muscle-derived cell line: biochemical, cellular and electrophysiological characterization

Excitation–contraction coupling is the physiological mechanism occurring in muscle cells whereby an electrical signal sensed by the dihydropyridine receptor located on the transverse tubules is transformed into a chemical gradient (Ca²⁺ increase) by activation of the ryanodine receptor located on the sarcoplasmic reticulum membrane. In the present study, we characterized for the first time the excitation–contraction coupling machinery of an immortalized human skeletal muscle cell line. Intracellular Ca²⁺ measurements showed a normal response to pharmacological activation of the ryanodine receptor, whereas 3D-SIM (super-resolution structured illumination microscopy) revealed a low level of structural organization of ryanodine receptors and dihydropyridine receptors. Interestingly, the expression levels of several transcripts of proteins involved in Ca²⁺ homoeostasis and differentiation indicate that the cell line has a phenotype closer to that of slow-twitch than fast-twitch muscles. These results point to the potential application of such human muscle-derived cell lines to the study of neuromuscular disorders; in addition, they may serve as a platform for the development of therapeutic strategies aimed at correcting defects in Ca²⁺ homoeostasis due to mutations in genes involved in Ca²⁺ regulation.