Two-dimensional model of calcium waves reproduces the patterns observed in Xenopus oocytes

Abstract

Biological excitability enables the rapid transmission of physiological signals over distance. Using confocal fluorescence microscopy, we previously reported circular, planar, and spiral waves of Ca2+ in Xenopus laevis oocytes that annihilated one another upon collision. We present experimental evidence that the excitable process underlying wave propagation depends on Ca2+ diffusion and does not require oscillations in inositol (1,4,5)trisphosphate (IP3) concentration. Extending an existing ordinary differential equation (ODE) model of Ca2+ oscillations to two spatial dimensions, we develop a partial differential equation (PDE) model of Ca2+ excitability. The model assumes that cytosolic Ca2+ couples neighboring Ca2+ release sites. This simple PDE model qualitatively reproduces our experimental observations.

Diffusion of inositol 1,4,5-trisphosphate but not Ca2+ is necessary for a class of inositol 1,4,5-trisphosphate-induced Ca2+ waves.

“…Because the effective diffusion constant for Ca2+ is much smaller than that of IP3 (9), it has been argued that diffusion of Ca2+ can explain the speed of the wave (10), and recently mathematical models have been used to explore the role of diffusion in these waves (4,11,12). Here we report calculations with a realistic model of IP3-induced Ca2+ oscillations (13), which when combined with the diffusion of Ca2+ and IP3 can generate wave trains that are primarily kinematic in nature-i.e., they do not require bulk movement of Ca2+ (14-16).…”

“…way, and Clapham, Lechleiter and colleagues (4) have documented a rich variety of dynamical patterns and spiral waves generated by nonhydrolyzable analogues of IP3. In hamster eggs, experiments have demonstrated that inactivating the IP3 receptor/Ca2+ channel (IP3R) with monoclonal antibodies is sufficient to eliminate fertilization-induced Ca2+ waves (5).…”

“…Recent experiments with pituitary gonadotrophs (6) and pancreatic acinar cells (7,8) suggest that similar mechanisms also may be functioning in these secretory cells. Although the biological function of Ca2+ waves is not known, their ubiquity in certain cell types, including fertilized egg cells (5), makes understanding their mode (or modes) of propagation an important problem. Because the effective diffusion constant for Ca2+ is much smaller than that of IP3 (9), it has been argued that diffusion of Ca2+ can explain the speed of the wave (10), and recently mathematical models have been used to explore the role of diffusion in these waves (4,11,12). Here we report calculations with a realistic model of IP3-induced Ca2+ oscillations (13), which when combined with the diffusion of Ca2+ and IP3 can generate wave trains that are primarily kinematic in nature-i.e., they do not require bulk movement of Ca2+ (14-16).…”

Submaximal stimulation of porcine endothelial cells causes focal Ca2+ elevation beneath the cell membrane

“…Adapting the idea of the superficial buffer barrier (SBB) introduced in smooth muscle cells to endothelial cells, we studied whether under weak stimulation with a physiological bradykinin concentration (< 2 nmol l¢; Linz, Wiemer & Sch olkens, 1996) or sodium fluoride, vectorial Ca¥ release towards the cell membrane from superficial endoplasmic reticulum (SER) occurs which is restricted to a discrete subplasmalemmal area by plasma membrane Na¤-Ca¥ exchange activity. Subplasmalemmal [Ca¥] ([Ca¥]sp) and bulk [Ca¥] ([Ca¥]b) were simultaneously recorded using Calcium Green-1 to measure predominantly [Ca¥]b (Girard, L uckhoff, Lechleiter, Sneyd & Clapham, 1992) and FFP-18 to estimate changes in [Ca¥]sp (Etter et al 1996). Distribution of endothelial ER was investigated using laser scanning (confocal) and deconvolution microscopy.…”

Characterization of Calcium Translocation across the Plasma Membrane of Primary Osteoblasts Using a Lipophilic Calcium-sensitive Fluorescent Dye, Calcium Green C18

“…In cultured osteoblasts, Calcium Green C 18 appears to be localized along the entire plasma membrane, except for regions associated with the coverslip. Ca 2ϩ specificity is indicated since the calcium greens have been shown to preferentially bind calcium (Girard et al, 1992). Further, little fluorescence was observed under the chosen confocal settings when cells were bathed with RCBSS, which intrinsically contained trace amounts of Ca 2ϩ .…”