Functional and Biochemical Properties of Ryanodine Receptor Type 1 Channels from Heterozygous R163C Malignant Hyperthermia-Susceptible Mice

Background FKBP12 is a protein that is closely associated with the ryanodine receptor type 1 of skeletal muscle and modulates Ca2+ release by the channel. The immunosuppressants FK506 and rapamycin both bind to FKBP12 and in turn dissociate the protein from the ryanodine receptor. By treating healthy human skeletal muscle strips with FK506 or rapamycin and then subjecting the strips to the caffeine-halothane contracture test, this study determined that FK506 and rapamycin alter the sensitivity of the muscle strip to halothane, caffeine, or both. Methods Skeletal muscle strips from 10 healthy persons were incubated in Krebs medium equilibrated with a 95% oxygen and 5% carbon dioxide mixture, which contained either 12 microM FK506 (n = 8) or 12 microM rapamycin (n = 6), for 15 min at 37 degrees C. The strips were subjected to the caffeine-halothane contracture test for malignant hyperthermia according to the European Malignant Hyperthermia Group protocol. Results Treatment of normal skeletal muscle strips with FK506 and rapamycin resulted in halothane-induced contractures of 0.44+/-0.16 g and 0.6+/-0.49 g, respectively, at 2% halothane. Conclusions The results obtained show that pre-exposure of healthy skeletal muscle strips to either FK506 or rapamycin is sufficient to give rise to halothane-induced contractures. This is most likely caused by destabilization of Ca2+ release by the ryanodine receptor as a result of the dissociation of FKBP12. This finding suggests that a mutation in FKBP12 or changes in its capacity to bind to the ryanodine receptor could alter the halothane sensitivity of the skeletal muscle ryanodine receptor and thereby predispose the person to malignant hyperthermia.

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Heat hypersensitivity of ryanodine receptor type 1 mutants implicated in malignant hyperthermia

10.1101/2020.10.29.351452 ◽

2020 ◽

Author(s):

Kotaro Oyama ◽

Vadim Zeeb ◽

Toshiko Yamazawa ◽

Takashi Murayama ◽

Hideto Oyamada ◽

...

Keyword(s):

Malignant Hyperthermia ◽

Ryanodine Receptor ◽

Positive Feedback ◽

Intracellular Signaling ◽

Feedback Loop ◽

Local Heat ◽

Receptor Type ◽

Positive Feedback Loop ◽

Hek 293

AbstractCellular heat-sensing is a universal strategy for avoiding thermal damage and adapting to environments by regulating thermogenic activities. If heat-sensing results in the acceleration of processes governing cellular thermogenesis, hyperthermia can occur. However, how this positive feedback loop contributes to hyperthermia development, especially the gap between heat-sensing and thermogenesis, remains largely unknown. Here, we show that an optically controlled local heat pulse induces an intracellular Ca2+ burst in cultured HEK 293 cells overexpressing ryanodine-receptor-type-1 (RyR1) mutants related to the life-threatening illness malignant hyperthermia (MH), and that the Ca2+ burst originates from heat-induced Ca2+-release (HICR) because of the mutant channels’ heat hypersensitivity. Furthermore, the heat hypersensitivity of the four RyR1 mutants was ranked, highlighting the complexity of MH. Our findings reveal the novel cellular heat-sensing mechanism, HICR, is essential for the functional positive feedback loop causing MH, suggesting a well-tuned HICR is fundamental for heat-mediated intracellular signaling.

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