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Ryanodine receptor in different malignant hyperthermia-susceptible porcine muscles
J M Ervasti1, M A Strand, T P Hanson
1Department of Biochemistry, University of Minnesota, St. Paul 55108.
Abstract:
The sarcoplasmic reticulum (SR) ryanodine receptor was studied in SR vesicles isolated from the vastus intermedius skeletal muscle and cardiac muscle of malignant hyperthermia-susceptible (MHS) and normal pigs. MHS and normal heavy SR preparations isolated from the vastus intermedius muscle had similar yields, polyacrylamide gel electrophoretic patterns, Ca2(+)-ATPase activities, mitochondrial enzyme activities, calsequestrin contents, and maximal [3H]ryanodine-binding activities. However, while half-maximal calcium concentrations (Ca0.5) for stimulation of MHS and normal vastus intermedius SR [3H]ryanodine binding were not significantly different, the Ca0.5 for inhibition of [3H]ryanodine binding to MHS vastus intermedius SR (76 +/- 17 microM) was significantly greater than to normal SR (16 +/- 9 microM). MHS vastus intermedius SR also exhibited a significantly lower Kd value (62 +/- 15 nM) for [3H]ryanodine binding compared with normal SR (Kd = 284 +/- 102 nM). These values for MHS and normal vastus intermedius SR are similar to those reported using SR isolated from a muscle composed of predominantly fast-twitch fibers, indicating the similarity of the ryanodine receptor in fast- and slow-twitch skeletal muscles. In contrast, there were no differences in the properties of the ryanodine receptor of porcine cardiac SR isolated from MHS and normal pigs. We therefore conclude that there is a defect in the SR ryanodine receptor of both slow- and fast-twitch skeletal muscle fiber types but not in cardiac muscle of MHS individuals.
Insights
Malignant hyperthermia-susceptible pigs have a defect in the skeletal muscle ryanodine receptor, affecting both fast- and slow-twitch fibers. This defect was not observed in their cardiac muscle ryanodine receptors.
Area of Science:
- Physiology
- Biochemistry
- Molecular Biology
Background:
- Malignant hyperthermia (MH) is a severe pharmacogenetic disorder triggered by volatile anesthetics and succinylcholine.
- The ryanodine receptor (RyR) is a calcium release channel critical for muscle excitation-contraction coupling.
- Defects in the skeletal muscle ryanodine receptor (RyR1) are linked to MH susceptibility.
Purpose of the Study:
- To investigate the properties of the sarcoplasmic reticulum (SR) ryanodine receptor in skeletal and cardiac muscle of malignant hyperthermia-susceptible (MHS) pigs.
- To determine if MHS affects the ryanodine receptor in different muscle fiber types (fast-twitch vs. slow-twitch) and in cardiac muscle.
Main Methods:
- Isolation of SR vesicles from vastus intermedius (skeletal) and cardiac muscle of MHS and normal pigs.
- Characterization of SR preparations, including yield, protein composition, enzyme activities, and calsequestrin content.
- Measurement of [3H]ryanodine binding to assess ryanodine receptor properties, including affinity (Kd) and sensitivity to calcium (Ca0.5).
Main Results:
- Skeletal muscle SR from MHS pigs showed altered ryanodine receptor properties, including increased sensitivity to calcium inhibition (higher Ca0.5) and higher affinity for ryanodine (lower Kd) compared to normal pigs.
- These alterations in skeletal muscle ryanodine receptor were consistent across fast- and slow-twitch fiber types.
- No significant differences in ryanodine receptor properties were found in cardiac SR between MHS and normal pigs.
Conclusions:
- A defect exists in the skeletal muscle ryanodine receptor of MHS pigs, impacting both fast- and slow-twitch muscle fibers.
- This defect in the skeletal ryanodine receptor is specific to muscle tissue and does not extend to the cardiac ryanodine receptor.
- The findings highlight a specific molecular abnormality in skeletal muscle RyR1 as the cause of MH susceptibility in pigs.