Mice with R2509C-RYR1 mutation exhibit dysfunctional Ca2+ dynamics in primary skeletal myocytes

Area of Science:

• Muscle Physiology
• Molecular Biology
• Genetics

Background:

• Type 1 ryanodine receptor (RYR1) is crucial for skeletal muscle excitation-contraction coupling.
• RYR1 mutations cause muscle diseases like malignant hyperthermia (MH), a disorder of Ca2+-induced Ca2+ release (CICR).
• Previous studies linked volatile anesthetics to MH-like episodes via enhanced CICR in heterozygous R2509C-RYR1 mice.

Purpose of the Study:

• Investigate Ca2+ dynamics in skeletal muscle cells from homozygous R2509C-RYR1 mice.
• Characterize the impact of RYR1 mutations on Ca2+ handling and muscle function.
• Determine the gene-dose-dependent effects of the R2509C mutation on RYR1 function.

Main Methods:

• Generated primary cultured skeletal myocytes from wild type (WT), heterozygous, and homozygous R2509C-RYR1 mice.
• Utilized electron microscopy to assess sarcomere length.
• Measured resting intracellular Ca2+ concentration and spontaneous Ca2+ transients.
• Employed infrared laser-based microheating to induce Ca2+ transients.

Main Results:

• Homozygous R2509C-RYR1 myocytes exhibited shortened sarcomere length and absent spontaneous Ca2+ transients and contractions.
• Resting intracellular Ca2+ was elevated in homozygous myocytes, potentially due to reduced SR Ca2+ content.
• Heterozygous myocytes displayed larger heat-induced Ca2+ transients compared to WT myocytes.
• No differences in cellular morphology were observed between WT and mutant myocytes.

Conclusions:

• The R2509C mutation in RYR1 causes dysfunctional Ca2+ dynamics in a gene-dose-dependent manner.
• This RYR1 dysfunction contributes to MH-like episodes in heterozygous mice and embryonic lethality in homozygous mice.
• Findings highlight the critical role of RYR1 Ca2+ release channel function in skeletal muscle health.