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Abnormal sarcoplasmic reticulum ryanodine receptor in malignant hyperthermia
J R Mickelson1, E M Gallant, L A Litterer
1Department of Veterinary Biology, University of Minnesota, St. Paul 55108.
Abstract:
Previous studies have demonstrated that skeletal muscle from individuals susceptible to malignant hyperthermia (MH) has a defect associated with the mechanism of calcium release from its intracellular storage sites in the sarcoplasmic reticulum (SR). In this report we demonstrate that the [3H]ryanodine receptor of isolated MH-susceptible (MHS) porcine heavy SR exhibits an altered Ca2+ dependence of [3H]ryanodine binding at the low affinity Ca2+ site as well as a lower Kd for ryanodine (92 versus 265 nM) when compared to normal porcine SR. The Bmax of the normal and MHS [3H] ryanodine receptor (9.3-12.6 pmol/mg) was not significantly different, and analysis of MHS and normal SR proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis did not reveal a significant difference in the intensity of Coomassie Blue staining of the spanning protein/ryanodine receptor region of the gels (Mr greater than 300,000). We also find that MHS porcine muscle intact fiber bundles exhibit a 5-10-fold lower ryanodine threshold for twitch and tetanus inhibition, and contracture onset when compared to normal muscle. Since the SR ryanodine receptor is a calcium release channel as well as a component intimately involved in transverse tubule-SR communication, abnormalities in the skeletal muscle ryanodine receptor may be responsible for the abnormal SR calcium release and contractile properties demonstrated by MHS muscle.
Insights
Malignant hyperthermia (MH) susceptible muscle has altered ryanodine receptor calcium binding and function. These defects in the sarcoplasmic reticulum (SR) ryanodine receptor may explain abnormal calcium release in MH-susceptible muscle.
Area of Science:
- Physiology
- Molecular Biology
- Pharmacology
Background:
- Malignant hyperthermia (MH) is a pharmacogenetic disorder of skeletal muscle.
- Individuals susceptible to MH exhibit defects in intracellular calcium release from the sarcoplasmic reticulum (SR).
Purpose of the Study:
- To investigate the properties of the ryanodine receptor (RyR) in MH-susceptible (MHS) porcine skeletal muscle.
- To determine if alterations in the RyR contribute to the abnormal calcium handling in MHS muscle.
Main Methods:
- Isolated MHS and normal porcine heavy SR were used for [3H]ryanodine binding assays.
- Ryanodine binding affinity (Kd) and capacity (Bmax) were analyzed.
- SR proteins were analyzed by SDS-PAGE.
- Intact MHS and normal porcine muscle fiber bundles were studied for ryanodine effects on contracture and inhibition.
Main Results:
- MHS porcine SR exhibited altered Ca2+ dependence of [3H]ryanodine binding at the low affinity Ca2+ site.
- MHS porcine SR showed a lower Kd for ryanodine (92 vs. 265 nM) compared to normal SR.
- No significant difference in Bmax or SR protein staining was observed between MHS and normal SR.
- MHS muscle fiber bundles displayed a 5-10 fold lower ryanodine threshold for twitch/tetanus inhibition and contracture onset.
Conclusions:
- Abnormalities in the skeletal muscle ryanodine receptor may underlie the defective SR calcium release in MHS muscle.
- The SR ryanodine receptor, a calcium release channel, is implicated in transverse tubule-SR communication.
- Altered RyR function in MHS muscle contributes to abnormal muscle contractile properties.