Abstract
Using a newly developed microfluidic chamber, we have demonstrated in vitro that Ca(2+) functions as a chemoattractant of aggregation-competent Dictyostelium discoideum amoebae, that parallel spatial gradients of cAMP and Ca(2+) are more effective than either alone, and that cAMP functions as a stronger chemoattractant than Ca(2+). Effective Ca(2+) gradients are extremely steep compared with effective cAMP gradients. This presents a paradox because there is no indication to date that steep Ca(2+) gradients are generated in aggregation territories. However, given that Ca(2+) chemotaxis is co-acquired with cAMP chemotaxis during development, we speculate on the role that Ca(2+) chemotaxis might have and the possibility that steep, transient Ca(2+) gradients are generated during natural aggregation in the interstitial regions between cells.
Highlights
Calcium (Ca2+) is ubiquitous in the environment of free-living cells as well as in cells in the tissues of plants and animals (Petersen et al, 2005; Case et al, 2007)
The two fluids were pumped through ports a and b, respectively, meeting at an interface (Fig. 1B) where the adjacent fluids were directed through a single square channel containing a sequence of chevrons etched into the ceiling of the square tube (Fig. 1C); these chevrons acted as micromixers mediating rapid and controlled mixing in a short path perpendicular to flow (Kaplan et al, 2004; Golden et al, 2007)
The channel is a square tube with sides of 300 m and a length of 28 mm, shown in blue Two programmable pumps control the flow rates from reservoirs a and b. (B) The interface of solutions a and b can be visualized by excitation of fluorescein at the intersection of the inlet ports with the channel
Summary
Calcium (Ca2+) is ubiquitous in the environment of free-living cells as well as in cells in the tissues of plants and animals (Petersen et al, 2005; Case et al, 2007). Evidence suggests that free extracellular Ca2+ might play a role as a chemoattractant in addition to cell-type-specific chemoattractants in a variety of developmental processes, including embryonic development (Adams et al, 2006; Chattopadhyay et al, 2007; Reitz et al, 1977), wound healing (Menon et al, 1985; Morris and Chan, 2007), angiogenesis (Aguirre et al, 2010), the immune response (Olszak et al, 2000) and tissue maintenance (Quarles et al, 1997). Brokaw (Brokaw, 1974) demonstrated that bracken fern spermatozoids undergo chemotaxis in combinatorial gradients of Ca2+ and bimalate Together, these observations suggest that chemotaxis in spatial gradients of Ca2+ might be a general phenomenon conserved throughout the eukaryotic world in cells that have, during evolution, acquired chemotaxis to more specialized cell-type-specific attractants
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