Related Experiment Videos
An electron paramagnetic resonance study of skeletal muscle membrane fluidity in malignant hyperthermia
J M Ervasti1, J R Mickelson, S M Lewis
1Department of Biochemistry, University of Minnesota, St. Paul 55108.
Abstract:
Skeletal muscle sarcolemma (SL), transverse tubule (TT) and heavy sarcoplasmic reticulum (HSR) membranes were isolated from malignant hyperthermia susceptible (MHS) and normal pigs, and the rotational dynamics of lipid hydrocarbon chain motion was examined by electron paramagnetic resonance (EPR) spectroscopy. The stearic acid spin probe 16-SASL was incorporated into MHS and normal membranes and both the order parameter (S) and effective correlation time (tau r) of probe motion were calculated from spectra recorded over the temperature range of 2 to 40 degrees C. At any given temperature, TT membranes exhibited significantly greater values for both the S and tau r of probe motion than did SL, which exhibited significantly greater values than did HSR membranes. The order of decreasing S and tau r values for 16-SASL mobility correlated with the decreasing cholesterol content of these membranes (TT greater than SL greater than HSR), however there was no difference in the S or tau r values for a given membrane fraction isolated from both MHS and normal muscle. Arrhenius plots of 16-SASL mobility in SL, TT and HSR were linear from 2 to 40 degrees C, indicating no abrupt thermotropic change in the lipid hydrocarbon phase of any of the membrane types studied. Apparent activation energies (Ea), calculated from the Arrhenius plots, were similar for MHS and normal membranes derived from a given cellular location. However, the Ea of probe motion for TT membranes (2.3 +/- 0.1 and 2.4 +/- 0.1 kcal/mol/degree for MHS and normal, respectively) was significantly less than for SL (3.4 +/- 0.4 and 2.9 +/- 0.1 kcal/mol/degree for MHS and normal, respectively) which, in turn, was significantly less than the Ea for HSR (3.7 +/- 0.1 and 3.7 +/- 0.1 kcal/mol/degree for MHS and normal, respectively). Since 16-SASL motion was similar in MHS and normal membranes, we conclude that there is no evidence for a generalized membrane defect affecting lipid mobility in these MHS muscle membranes.
Insights
Malignant hyperthermia susceptible (MHS) muscle membranes show no differences in lipid mobility compared to normal muscle membranes. Electron paramagnetic resonance spectroscopy revealed similar lipid dynamics across skeletal muscle sarcolemma, transverse tubules, and sarcoplasmic reticulum in both MHS and normal pigs.
Area of Science:
- Biophysics
- Cell Biology
- Muscle Physiology
Background:
- Malignant hyperthermia is a pharmacogenetic disorder affecting skeletal muscle.
- Understanding membrane properties in malignant hyperthermia susceptible (MHS) muscle is crucial for identifying potential defects.
Purpose of the Study:
- To investigate the rotational dynamics of lipid hydrocarbon chain motion in skeletal muscle membranes from MHS and normal pigs.
- To determine if MHS muscle membranes exhibit altered lipid mobility compared to normal membranes.
Main Methods:
- Isolation of skeletal muscle sarcolemma (SL), transverse tubule (TT), and heavy sarcoplasmic reticulum (HSR) membranes.
- Electron paramagnetic resonance (EPR) spectroscopy using a stearic acid spin probe (16-SASL).
- Calculation of order parameter (S) and effective correlation time (tau r) over a temperature range of 2-40°C.
Main Results:
- TT membranes showed higher order (S) and slower motion (tau r) than SL, which were higher than HSR membranes, correlating with cholesterol content.
- No significant differences in S or tau r were observed for any membrane fraction between MHS and normal pigs.
- Apparent activation energies (Ea) for lipid motion varied significantly between membrane types (TT < SL < HSR) but were similar between MHS and normal pigs.
Conclusions:
- Lipid mobility in SL, TT, and HSR membranes is not altered in MHS pigs compared to normal pigs.
- The findings do not support a generalized membrane defect affecting lipid mobility in MHS muscle.
- Differences in activation energy suggest distinct lipid environments and dynamics across different muscle membrane compartments.