Related Experiment Videos
Evidence for intraluminal Ca++ regulatory site defect in sarcoplasmic reticulum from malignant hyperthermia pig
1University of Texas Health Science Center, Department of Anesthesiology, Houston, Texas.
Abstract:
Malignant hyperthermia (MH) is a pharmacogenetic disease of humans and various animal species that predisposes to a life-threatening, anesthetic agent-induced syndrome. MH is thought to be a consequence of abnormal, sustained increases in myoplasmic Ca++ and sarcoplasmic reticulum (SR) membranes from MH muscle have been shown to have a Ca++ release channel defect. In the present study we have tested a hypothesis that the abnormal Ca++ release mechanism in MH can be expressed when Ca++ is loaded in the presence of pyrophosphate. SR membrane vesicles isolated from normal and MH pig muscle were loaded with Ca++ in the presence and absence of pyrophosphate until Ca(++)-induced Ca++ release occurred. Under both circumstances the threshold amount of Ca++ loaded until Ca++ release occurred was lower in the SR from MH pig skeletal muscle. This difference in amount of Ca++ preload is not explained by results obtained comparing rates of Ca++ uptake, number of ryanodine binding sites or the amounts of calsequestrin among SR vesicles from MH and normal muscle. We conclude from this study that use of pyrophosphate for Ca++ loading does not ablate the abnormal Ca++ release in SR from MH muscle, suggesting the study can be done on small amounts of SR from biopsied human muscle. The data also suggest that abnormality in an intraluminal, low affinity Ca++ binding site regulating Ca++ release occurs in the SR membrane of MH pig muscle.
Insights
Malignant hyperthermia (MH) involves abnormal calcium release from muscle stores. This study shows pyrophosphate loading doesn't mask this defect, suggesting a new diagnostic approach for MH.
Area of Science:
- Pharmacogenetics
- Molecular Biology
- Muscle Physiology
Background:
- Malignant hyperthermia (MH) is a dangerous genetic disorder triggered by anesthesia.
- It's linked to faulty calcium (Ca++) regulation in muscle cells, specifically within the sarcoplasmic reticulum (SR).
- Previous research indicates a defect in the SR's Ca++ release channel in MH.
Purpose of the Study:
- To investigate if pyrophosphate affects abnormal Ca++ release in MH.
- To determine if this method can be used for diagnosing MH in humans.
Main Methods:
- SR membrane vesicles were isolated from normal and MH pig muscle.
- Vesicles were loaded with Ca++ with and without pyrophosphate.
- Ca++-induced Ca++ release was measured under these conditions.
Main Results:
- SR from MH pigs released Ca++ at lower thresholds, even with pyrophosphate.
- Pyrophosphate loading did not obscure the abnormal Ca++ release in MH muscle.
- Differences in Ca++ uptake, ryanodine binding, and calsequestrin did not explain the findings.
Conclusions:
- Pyrophosphate does not mask the abnormal Ca++ release characteristic of MH.
- This suggests pyrophosphate-assisted Ca++ loading may be viable for studying small human muscle biopsies.
- An abnormality in an intraluminal, low-affinity Ca++ binding site is implicated in MH.