Luminal Ca 2+ dynamics during IP 3 R mediated signals

Abstract

The role of cytosolic Ca2+ on the kinetics of Inositol 1,4,5-triphosphatereceptors (IP3Rs) and on the dynamics of IP3R-mediated Ca2+ signals has been studiedat large both experimentally and by modeling. The role of luminal Ca2+ has not beeninvestigated with that much detail although it has been found that it is relevant forsignal termination in the case of Ca2+ release through ryanodine receptors. In thiswork we present the results of observing the dynamics of luminal and cytosolic Ca2+simultaneously in Xenopus laevis oocytes. Combining observations and modeling weconclude that there is a rapid mechanism that guarantees the availability of free Ca2+in the lumen even when a relatively large Ca2+ release is evoked. Comparing thedynamics of cytosolic and luminal Ca2+ during a release, we estimate that they areconsistent with a 80% of luminal Ca2+being buffered. The rapid availability of freeluminal Ca2+ correlates with the observation that the lumen occupies a considerablevolume in several regions across the images.