Related Experiment Videos
Myotoxin a reduces the threshold for calcium-induced calcium release in skeletal muscle
M L Yudkowsky1, J Beech, J E Fletcher
1Department of Anesthesiology, Hahnemann University, Philadelphia, PA 19102.
Abstract:
Myotoxin a, isolated from the venom of the prairie rattlesnake Crotalus viridis viridis, induces necrosis in skeletal muscle. In isolated organelles, it has been reported that myotoxin a reduces Ca2+ uptake into the sarcoplasmic reticulum. The effects of the toxin on Ca2+ regulation were examined in heavy sarcoplasmic reticulum fractions from human and equine skeletal muscle. Ca2+ uptake and release (the threshold of Ca(2+)-induced Ca2+ release) were examined by dual wavelength spectrophotometry. The toxin lowered the threshold of Ca(2+)-induced Ca2+ release in a dose-dependent manner (1-10 microM) and this effect was antagonized by ruthenium red, a Ca2+ release channel blocker. Ca2+ uptake into equine heavy sarcoplasmic reticulum was not decreased by myotoxin a (10 microM) when Ca2+ release was blocked by ruthenium red. [3H]Ryanodine binding to equine heavy sarcoplasmic reticulum was converted from a relatively low affinity state to a higher affinity state by myotoxin a. These results suggest that the dominant effect of myotoxin a is to increase the Ca2+ sensitivity for the opening of the calcium release channel (ryanodine receptor). Myotoxin a may prove to be a useful tool to probe the modulation of calcium release in sarcoplasmic reticulum fractions.
Insights
Prairie rattlesnake myotoxin a disrupts skeletal muscle calcium regulation by increasing the sensitivity of the calcium release channel. This venom component affects calcium release, not uptake, in sarcoplasmic reticulum.
Area of Science:
- Biochemistry
- Molecular Biology
- Toxicology
Background:
- Myotoxin a from Crotalus viridis viridis venom causes skeletal muscle necrosis.
- Previous studies suggest myotoxin a may interfere with calcium (Ca2+) uptake into the sarcoplasmic reticulum.
Purpose of the Study:
- To investigate the effects of myotoxin a on Ca2+ regulation in human and equine skeletal muscle sarcoplasmic reticulum.
- To determine if myotoxin a affects Ca2+ uptake or Ca2+ release from the sarcoplasmic reticulum.
Main Methods:
- Heavy sarcoplasmic reticulum fractions were isolated from human and equine skeletal muscle.
- Ca2+ uptake and Ca(2+)-induced Ca2+ release were measured using dual wavelength spectrophotometry.
- [3H]Ryanodine binding assays were performed to assess ryanodine receptor activity.
Main Results:
- Myotoxin a dose-dependently decreased the threshold for Ca(2+)-induced Ca2+ release.
- Ruthenium red, a Ca2+ release channel blocker, antagonized the effect of myotoxin a on Ca2+ release.
- Myotoxin a did not decrease Ca2+ uptake when Ca2+ release was blocked.
- [3H]Ryanodine binding indicated myotoxin a increased the affinity of the ryanodine receptor.
Conclusions:
- Myotoxin a primarily enhances the Ca2+ sensitivity of the calcium release channel (ryanodine receptor) in skeletal muscle sarcoplasmic reticulum.
- The toxin's effect on Ca2+ regulation involves modulating Ca2+ release rather than uptake.
- Myotoxin a could be a valuable research tool for studying sarcoplasmic reticulum calcium release modulation.