Changes in Ca(2+) Removal Can Mask the Effects of Geometry During IP(3)R Mediated Ca(2+) Signals

Calcium (Ca(2+)) signals are ubiquitous. Most intracellular Ca(2+) signals involve the release of Ca(2+) from the endoplasmic reticulum (ER) through Inositol 1,4,5-Trisphosphate Receptors (IP(3)Rs). The non-uniform spatial organization of IP(3)Rs and the fact that their individual openings are coupled via cytosolic Ca(2+) are key factors for the variety of spatio-temporal distributions of the cytosolic [Ca(2+)] and the versatility of the signals. In this paper we combine experiments performed in untreated and in progesterone-treated Xenopus laevis oocytes and mathematical models to investigate how the interplay between geometry (the IP(3)R spatial distribution) and dynamics (the processes that characterize the release, transport, and removal of cytosolic Ca(2+)) affects the resulting signals. Signal propagation looks more continuous and spatially uniform in treated (mature) than in untreated (immature) oocytes. This could be due to the different underlying IP(3)R spatial distribution that has been observed in both cell types. The models, however, show that the rate of cytosolic Ca(2+) removal, which is also different in both cell types, plays a key role affecting the coupling between Ca(2+) release sites in such a way that the effect of the underlying IP(3)R spatial distribution can be modified.