Simultaneous measurements of changes in sarcoplasmic reticulum and cytosolic [Ca2+] in rat uterine smooth muscle cells


Corresponding author S. Wray: Physiological Laboratory, University of Liverpool, Crown Street, Liverpool L69 3BX, UK., Email:


  • 1The role of the sarcoplasmic reticulum (SR) was investigated in spontaneous and agonist-induced uterine Ca2+ transients, by combining low- (mag-fluo-4) and high-affinity (fura-2) indicators to measure intraluminal SR ([Ca2+]L) and cytosolic ([Ca2+]i) calcium concentration, simultaneously, in single smooth muscle cells from pregnant rat uterus.
  • 2Carbachol or ATP, in the absence of extracellular Ca2+, decreased [Ca2+]L and increased [Ca2+]i. Although some replenishment (around 50 %) occurred in its absence, extracellular Ca2+ was required for full replenishment of the SR Ca2+.
  • 3In 4/15 cells, ATP evoked oscillations of [Ca2+]i. These were accompanied by successive release and re-uptake of SR Ca2+. Inhibition of the SR Ca2+-ATPase with thapsigargin abolished the oscillations and luminal changes.
  • 4Spontaneous [Ca2+]i transients produced no detectable changes in [Ca2+]L. The larger [Ca2+]i transients evoked by high-K+ depolarisation increased [Ca2+]L. Spontaneous activity was inhibited when [Ca2+]L was increased.
  • 5These data show that it is possible to simultaneously measure SR and cytosolic [Ca2+], and to investigate their response to agonist application and spontaneous activity.