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Training-induced sarcoplasmic reticulum Ca2+ unloading occurs without Ca2+ influx.
Carol A Witczak1, Michael Sturek
1Department of Medical Pharmacology & Physiology, University of Missouri, Columbia, MO, USA.
Medicine and Science in Sports and Exercise
|July 15, 2005
Summary
Aerobic exercise training induces sarcoplasmic reticulum (SR) Ca2+ unloading in coronary smooth muscle. This phenomenon, crucial for cellular function, does not require extracellular Ca2+ influx in swine models.
Area of Science:
- Cardiovascular Physiology
- Smooth Muscle Biology
- Cellular Signaling
Background:
- Aerobic exercise training induces adaptations in coronary smooth muscle.
- A novel phenomenon, sarcoplasmic reticulum (SR) Ca2+ unloading, is observed.
- SR Ca2+ unloading involves time-dependent depletion and repletion of the SR Ca2+ store.
Purpose of the Study:
- To investigate the necessity of Ca2+ influx for SR Ca2+ unloading.
- To understand the mechanisms underlying exercise-induced SR Ca2+ unloading.
Main Methods:
- Male Yucatan swine were divided into sedentary and exercise-trained groups.
- Smooth muscle cells from coronary arteries were isolated and loaded with fura-2.
- SR Ca2+ content was measured by caffeine-induced Ca2+ release under varying extracellular Ca2+ concentrations.
Main Results:
- SR Ca2+ unloading was absent in sedentary swine.
- Exercise-trained swine exhibited SR Ca2+ depletion in both normal and Ca2+-free solutions.
- SR Ca2+ repletion occurred even without extracellular Ca2+, indicating internal Ca2+ cycling.
Conclusions:
- Extracellular Ca2+ influx is not required for exercise-induced SR Ca2+ unloading in coronary smooth muscle.
- Exercise training facilitates internal Ca2+ cycling between the SR and other intracellular stores.