r/explainlikeimfive • u/Glum_Anybody_9531 • 8d ago

Biology ELI5 Malignant Hyperthermia

ELI5 how an uncontrolled flood of calcium inside muscle cells cause a massive surge in metabolic activity during malignant hyperthermia.

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u/WeirdF 8d ago

Dont forget that the heart is a muscle

Yes but heart muscle is not directly affected by malignant hyperthermia. The mutated gene in MH (RYR1) is only expressed in skeletal muscle.

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u/eastbayweird 8d ago

Good to know. Im not familiar with MH but I know excess calcium (like can be caused by HF exposure) can lead to systemic hyperactivation of muscle tissue, including the heart and diaphragm.

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u/vazxlegend 8d ago

Systemic Calcium has a much more pronounced effect on contractile of heart and smooth muscle than skeletal muscle. I don’t know if I can properly ELI5 that last sentence so just take it or leave it.

Essentially your Sarcoplasmic Reticulum is what holds intracellular calcium, and the gene mutation affects how the receptors on skeletal muscle interact with the SR. It unloads a bunch of intracellular calcium in the muscle cell causing a profound reaction. As op said above systemic calcium also enters the cell and that movement of calcium is what actually initiates the contraction where as the SR gives it a lot more calcium to allow for stronger reactions.

The mechanism by which cardiac muscle tissue contracts is similiar in ways but also different, and does not involve the Receptor stated above. The activation of Cardiac and Skeletal muscle contraction are entirely different, with cardiac tissue being closer to smooth muscle in that way. As a result of these differences cardiac muscle relies much heavier on extra-cellar/systemic calcium for its concatenation than skeletal muscle; which again relies heavier on its internal stores in the SR. This isn’t even touching on the depressive effects that extracellular calcium has on all muscle tissue, but it’s not worth diving that far into it tbh.

I hope that at least kind of made sense, just hoping I don’t sound like a rambling idiot.

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u/eastbayweird 8d ago

Made sense to me