Training-induced sarcoplasmic reticulum Ca2+ unloading occurs without Ca2+ influx

Carol A. Witczak, Michael Sturek

Research output: Contribution to journalArticle

5 Scopus citations


Introduction: Aerobic exercise training elicits adaptations in coronary smooth muscle that result in a novel intracellular Ca2+ signaling phenomenon termed sarcoplasmic reticulum (SR) Ca2+ unloading. Sarcoplasmic reticulum Ca2+ unloading is defined as a time-dependent depletion and then repletion of the caffeine-sensitive SR Ca2+ store. Purpose: To determine whether Ca2+ influx is necessary to elicit SR Ca2+ unloading. Methods: Male, Yucatan swine (8 months old) were maintained: 1) sedentary or 2) exercise trained (treadmill running performed 5 d·wk-1 for 16 wk). Smooth muscle cells were isolated from the right coronary artery and loaded with the intracellular Ca2+- indicator, fura-2. Sarcoplasmic reticulum Ca2+ content was assessed as the change in the caffeine (5 mM)-induced intracellular Ca2+ peak after a 2-, 5-, 8-, 11- or 13-min recovery from high K+ (depolarization)-induced Ca2+ influx in a physiological (2 mM) Ca2+ solution. The effect of Ca2+ influx on SR Ca2+ unloading was assessed by replacing the 2 mM Ca2+ solution with a virtually Ca 2+-free (100 nM) solution during the recovery period. Results: Consistent with previous studies, SR Ca2+ unloading was not observed in cells from sedentary swine. In cells from exercise-trained swine, SR Ca 2+ depletion was observed in both the 2 mM and Ca2+-free solutions, suggesting that Ca2+-induced Ca2+ release was not initiating SR Ca2+ unloading during the recovery period. In addition, the reloading of the SR Ca2+ store occurred even in the Ca2+-free solution, suggesting that exercise training facilitates an internal cycling of Ca2+ between the SR and another intracellular Ca2+ store. Conclusion: In coronary smooth muscle from male swine, Ca2+ influx is not necessary for the exercise training-induced phenomenon, SR Ca2+ unloading.

Original languageEnglish (US)
Pages (from-to)1119-1125
Number of pages7
JournalMedicine and Science in Sports and Exercise
Issue number7
StatePublished - Jul 1 2005


  • Ca-induced Ca release porcine
  • Ryanodine receptor
  • Superficial buffer barrier

ASJC Scopus subject areas

  • Public Health, Environmental and Occupational Health
  • Physical Therapy, Sports Therapy and Rehabilitation
  • Orthopedics and Sports Medicine

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