Observation and modeling of luminal Ca2+ dynamics during IP3R-mediated Ca2+ signals

LUCIA LOPEZ; SILVINA PONCE DAWSON

Conferencia; Latin American Conference on Mathematical Modeling of Biological Systems; 2015

The role of cytosolic Ca2+ on the kinetics of Inositol 1,4,5-triphosphate receptors (IP3Rs) and on the dynamics of IP3R-mediated Ca2+ signals has been studied at large both experimentally and by modeling. The role of luminal calcium has not been investigated with that much detail although it has been found that it is relevant for signal termination in the case of Ca2+ release through ryanodine receptors. In this work we present the results of observing the dynamics of luminal and cytosolic Ca2+ simultaneously in Xenopus Laevis oocytes. Combining observations and modeling we conclude 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 the dynamics of depletion and re-uptake we estimate that they are consistent with an 80% of luminal Ca2+ being buffered. The rapid availability of free luminal Ca2+ correlates well with the area to volume ratio of the space occupied by the lumen that we observe in the experiments.