In this study we report for the first time the functional properties of human myotubes isolated from patients harboring the native
RYR1 I4898T and R4893W mutations linked to
central core disease. We examined two aspects of myotube physiology, namely excitation-contraction and excitation-secretion coupling. Our results show that upon activation of the
ryanodine receptor (RYR), myotubes release
interleukin-6 (IL-6); this was dependent on de novo
protein synthesis and could be blocked by
dantrolene and
cyclosporine. Myotubes from the two patients affected by
central core disease showed a 4-fold increase in the release of the inflammatory
cytokine IL-6, compared with cells derived from control or
malignant hyperthermia susceptible individuals. All tested myotubes released
calcium from intracellular stores upon stimulation via surface membrane depolarization or direct RYR activation by 4-chloro-m-cresol. The functional impact on
calcium release of
RYR1 mutations linked to
central core disease or
malignant hyperthermia is different: human myotubes carrying the
malignant hyperthermia-linked
RYR1 mutation V2168M had a shift in their sensitivity to the RYR agonist 4-chloro-m-cresol to lower concentrations, whereas human myotubes harboring C-terminal mutations linked to
central core disease exhibited reduced [Ca2+]i increase in response to 4-chloro-m-cresol,
caffeine, and KCl. Taken together, these results suggest that abnormal release of
calcium via mutated RYR enhances the production of the inflammatory
cytokine IL-6, which may in turn affect signaling pathways responsible for the trophic status of muscle fibers.