Simultaneous measurements of changes in sarcoplasmic reticulum and cytosolic.
1. The 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. 2. Carbachol 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+. 3. In 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. 4. Spontaneous [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. 5. These data show that it is possible to simultaneously measure SR and cytosolic [Ca2+], and to investigate their response to agonist application and spontaneous activity.
Department of Physiology, University of Liverpool, Crown Street, Liverpool L69 3BX, UK.
A V
AV
Shmigol
D A
DA
Eisner
S
S
Wray
D000818:Animals; D016477:Artifacts; D002118:Calcium / Q000819:agonists / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D005260:Female; D008274:Magnesium / Q000378:metabolism; D009130:Muscle, Smooth / Q000166:cytology / Q000378:metabolism*; D009994:Osmolar Concentration; D051381:Rats; D017208:Rats, Wistar; D015203:Reproducibility of Results; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D014590:Uterine Contraction / Q000502:physiology; D014599:Uterus / Q000166:cytology / Q000378:metabolism*
D008274:Magnesium; D002118:Calcium