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Competition between oxalate and phosphate during active calcium accumulation by sarcoplasmic vesicles
Zeitschrift Fur Naturforschung. Section C, Biosciences
|March 1, 1977
Summary
Phosphate inhibits calcium uptake by sarcoplasmic reticulum vesicles, impacting muscle function. This occurs because phosphate prevents oxalate co-uptake, leading to altered calcium levels and ATPase activity.
Area of Science:
- Muscle Physiology
- Biochemistry
Background:
- Sarcoplasmic reticulum vesicles actively transport calcium.
- Calcium uptake is crucial for muscle contraction and relaxation.
Purpose of the Study:
- To investigate the effects of oxalate and phosphate on calcium uptake by sarcoplasmic reticulum vesicles.
- To elucidate the mechanism of phosphate-induced inhibition of calcium transport.
Main Methods:
- ATP-dependent active calcium uptake assays.
- Vesicle assays using sarcoplasmic reticulum.
- Measurement of anion and calcium accumulation.
Main Results:
- Sarcoplasmic reticulum vesicles accumulate calcium with either oxalate or phosphate, but not both simultaneously.
- Phosphate inhibits calcium uptake by preventing oxalate co-accumulation, leading to a 100-fold increase in intravesicular ionized calcium.
- Calcium-dependent ATPase activity parallels calcium uptake, indicating functional coupling.
Conclusions:
- Phosphate inhibits calcium transport into sarcoplasmic reticulum vesicles through competitive exclusion of oxalate.
- This inhibition is not due to increased membrane permeability but rather altered intravesicular calcium dynamics.
- The findings highlight the complex interplay between anions and calcium transport in muscle energetics.
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