Junctional membrane Ca 2+ dynamics in human muscle fibers are altered by malignant hyperthermia causative RyR mutation

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 115; no. 32; pp. 8215 - 8220
• Main Authors: Cully, Tanya R, Choi, Rocky H, Bjorksten, Andrew R, Stephenson, D George, Murphy, Robyn M, Launikonis, Bradley S
• Format: Journal Article
• Language: English
• Published: United States 07.08.2018
• Subjects: Adult; Biopsy; Calcium - chemistry; Calcium - metabolism; Cations, Divalent - chemistry; Cations, Divalent - metabolism; Cell Membrane - metabolism; Cell Membrane - pathology; Female; Fluorescent Dyes - chemistry; Humans; Intercellular Junctions - metabolism; Intercellular Junctions - pathology; Male; Malignant Hyperthermia - genetics; Malignant Hyperthermia - pathology; Mutation; Nanostructures - chemistry; Ryanodine Receptor Calcium Release Channel - genetics; Ryanodine Receptor Calcium Release Channel - metabolism; Sarcoplasmic Reticulum - metabolism; Sarcoplasmic Reticulum - pathology; Young Adult; ryanodine receptor; Ca2; t-system; malignant hyperthermia; human skeletal muscle
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1800490115

We used the nanometer-wide tubules of the transverse tubular (t)-system of human skeletal muscle fibers as sensitive sensors for the quantitative monitoring of the Ca -handling properties in the narrow junctional cytoplasmic space sandwiched between the tubular membrane and the sarcoplasmic reticulum cisternae in single muscle fibers. The t-system sealed with a Ca -sensitive dye trapped in it is sensitive to changes in ryanodine receptor (RyR) Ca leak, the store operated calcium entry flux, plasma membrane Ca pump, and sodium-calcium exchanger activities, thus making the sealed t-system a nanodomain Ca sensor of Ca dynamics in the junctional space. The sensor was used to assess the basal Ca -handling properties of human muscle fibers obtained by needle biopsy from control subjects and from people with a malignant hyperthermia (MH) causative RyR variant. Using this approach we show that the muscle fibers from MH-susceptible individuals display leakier RyRs and a greater capacity to extrude Ca across the t-system membrane compared with fibers from controls. This study provides a quantitative way to assess the effect of RyR variants on junctional membrane Ca handling under defined ionic conditions.