The effects of extracellular calcium on motility, pseudopod and uropod formation, chemotaxis, and the cortical localization of myosin II in Dictyostelium discoideum

Abstract

Extracellular Ca++, a ubiquitous cation in the soluble environment of cells both free living and within the human body, regulates most aspects of amoeboid cell motility, including shape, uropod formation, pseudopod formation, velocity and turning in Dictyostelium discoideum. Hence it affects the efficiency of both basic motile behavior and chemotaxis. Extracellular Ca++ is optimal at 10 mM. A gradient of the chemoattractant cAMP generated in the absence of added Ca++ only affects turning, but in combination with extracellular Ca++, enhances the effects of extracellular Ca++. Potassium, at 40 mM, can substitute for Ca++. Mg++, Mn++, Zn++ and Na+ cannot. Extracellular Ca++, or K+, also induce the cortical localization of myosin II in a polar fashion. The effects of Ca++, K+ or a cAMP gradient do not appear to be similarly mediated by an increase in the general pool of free cytosolic Ca++. These results suggest a model, in which each agent functioning through different signaling systems, converge to affect the cortical localization of myosin II, which in turn effects the behavioral changes leading to efficient cell motility and chemotaxis.

The IplA Ca++ Channel OfDictyostelium discoideumIs Necessary For Ca++, But Not cAMP Chemotaxis, And Plays A Fundamental Role In Natural Aggregation

“…3A,D Table S1). And as previously reported (Lusche et al, 2009;Lusche et al, 2011), increasing the Ca 2+ concentration in TB from 0 to 5 mM in the (Furuichi et al, 1989;Joseph, 1996;Foskett et al, 2007;Foskett, 2010;Mignery and Sudhof, 1990 absence of cAMP resulted in an increase in the directional persistence of translocating cells (Fig. 3A,E concentration in TB was increased to 10 mM ( Fig.…”

“…As we previously reported for parental Ax2 cells (Lusche et al, 2009), increasing the concentration of Ca 2+ in TB to 10 mM in a spatial gradient of cAMP caused an increase in the three motility parameters, instantaneous velocity (Fig. 4A,B), percentage of cells with instantaneous velocities of $9 mm/minute (Fig.…”

“…mechanoreception) (Fache et al, 2005;Lombardi et al, 2008). Together, these results suggested that IplA was a strong candidate for a cell surface molecule or a molecule in the signal transduction pathway that mediated the facilitating effects of extracellular Ca 2+ on motility and cAMP chemotaxis, and/or Ca 2+ chemotaxis (Lusche et al, 2009;Scherer et al, 2010). Here, we provide evidence that IplA plays selective roles in the extracellular effects of Ca 2+ on cell behavior.…”

“…3F,G). If IplA plays a selective role in the cationic facilitation of cell motility by Ca 2+ in the absence of cAMP, then cells of the null mutant iplA -and its parent strain Ax2 should exhibit no behavioral differences from wild-type cells when translocating in TB containing 40 mM K + , the facilitating concentration of this monovalent cation in the absence of added Ca 2+ (Lusche et al, 2009). This prediction is predicated on the discovery that K + , but not Ca 2+ , facilitation is mediated by Nhe1 .…”

“…For that reason, they must be present at optimum concentrations in the natural environment . For the soil amoeba Dictyostelium discoideum to achieve maximum velocity either the extracellular concentration of Ca 2+ must reach 10 mM or the concentration of K + reach 40 mM (Lusche et al, 2009;Lusche et al, 2011;Scherer et al, 2010). Moreover, for D. discoideum amoebae to orient in a spatial gradient of the chemoattractant cAMP, either Ca 2+ must reach 5 mM, or K + or Na + reach 15 mM (Lusche et al, 2009;Lusche et al, 2011).…”