The role of the sarcoplasmic reticulum as a Ca2+ sink in rat uterine smooth muscle cells
Article first published online: 7 SEP 2004
The Journal of Physiology
Volume 520, Issue 1, pages 153–163, October 1999
How to Cite
Shmigol, A. V., Eisner, D. A. and Wray, S. (1999), The role of the sarcoplasmic reticulum as a Ca2+ sink in rat uterine smooth muscle cells. The Journal of Physiology, 520: 153–163. doi: 10.1111/j.1469-7793.1999.00153.x
- Issue published online: 7 SEP 2004
- Article first published online: 7 SEP 2004
- (Received 5 May 1999; accepted after revision 6 July 1999)
- 1The mechanisms responsible for removing calcium ions from the cytoplasm were investigated in single rat uterine myocytes using indo-1.
- 2Trains of depolarizing voltage-clamp pulses increased [Ca2+]i. The rate of decay of [Ca2+]i was slowed by inhibition of the sarcoplasmic reticulum (SR) Ca2+-ATPase with cyclopiazonic acid (CPA). However, if the sarcolemmal Na+-Ca2+ exchanger and Ca2+-ATPase were inhibited then recovery of [Ca2+]i was abolished showing that the SR Ca2+-ATPase alone cannot produce decay of [Ca2+]i.
- 3In another series of experiments, Ca2+ release from the SR was induced with carbachol in a Ca2+-free solution. Under these conditions responses to repeated applications of carbachol could be obtained. In the presence of CPA, however, only the first application was effective. This suggests that the SR Ca2+-ATPase sequesters a significant amount of Ca2+ into the SR.
- 4CPA slowed the rate of decay of [Ca2+]i following carbachol addition by > 50%. Again, however, after a brief transient fall, decay was abolished when the Na+-Ca2+ exchanger and sarcolemmal Ca2+-ATPase were inhibited.
- 5These data show that, although the SR Ca2+-ATPase contributes to the decay of [Ca2+]i, it cannot function effectively in the absence of Ca2+ removal from the cell. These data are discussed in the context of the superficial buffer barrier model in which Ca2+ is taken up into the SR and then released very close to sarcolemmal Ca2+ extrusion sites, i.e. the SR acting in series with the surface membrane extrusion mechanisms. We also suggest that the amount of filling of the SR influences the rate of Ca2+ removal.