Functionally and spatially distinct Ca2+ stores are revealed in cultured vascular smooth muscle cells

Rachel Tribe, M L Borin, M P Blaustein

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Sarcoplasmic reticulum Ca2+ in vascular smooth muscle may be separated into at least two types of Ca2+ stores, one releasable by inositol 1,4,5-trisphosphate and the other releasable by caffeine and ryanodine. We employed digital imaging with fura-2 to study the effects of thapsigargin (which blocks Ca2+ sequestration in the inositol trisphosphate-sensitive store) and caffeine on the cytosolic free Ca2+ concentration ([Ca2+]cyt) in cultured arterial myocytes. These agents increased [Ca2+]cyt by depleting different Ca2+ stores in the absence of extracellular Ca2+. Moreover, Ca2+ could be transferred between the two stores, as prior application of caffeine, which alone evoked little or no rise in [Ca2+]cyt, significantly augmented the response to thapsigargin. Conversely, a substantial caffeine-induced rise in [Ca2+]cyt was observed only after the ability of the thapsigargin-sensitive Ca2+ store to sequester Ca2+ was inhibited. This suggests that the caffeine-sensitive store may have a thapsigargin-insensitive Ca(2+)-sequestration mechanism. To complement these fura-2 experiments, chlortetracycline was used to visualize the Ca2+ stores directly. The latter studies revealed spatial differences in the location of the thapsigargin-sensitive and caffeine-sensitive Ca2+ stores (measured as thapsigargin-sensitive and caffeine-sensitive chlortetracycline fluorescence). Thus, these two types of stores appear to be both functionally and spatially distinct.
Original languageEnglish
Pages (from-to)5908-12
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number13
Publication statusPublished - 21 Jun 1994


  • Animals
  • Aorta
  • Caffeine
  • Calcium
  • Calcium-Transporting ATPases
  • Cell Line
  • Cells, Cultured
  • Fetus
  • Inositol 1,4,5-Trisphosphate
  • Kinetics
  • Microscopy, Fluorescence
  • Muscle, Smooth, Vascular
  • Rats
  • Ryanodine
  • Terpenes
  • Thapsigargin
  • Time Factors

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