Diverse chemotactic responses of Dictyostelium discoideum amoebae in the developing (temporal) and stationary (spatial) concentration gradients of folic acid, cAMP, Ca2+ and Mg2+

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Abstract
The responses of Dictyostelium discoideum amoebae to developing (temporal) and stationary (spatial) gradients of folic acid, cAMP, Ca2+, and Mg2+ were studied using the methods of computer‐aided image analysis. The results presented demonstrate that the new type of experimental chambers used for the observation of single cells moving within the investigated gradients of chemoattractants permit time lapse recording of single amoebae and determination of the trajectories of moving cells. It was found that, besides folic acid and cAMP (natural chemoattractants for Dictyostelium discoideum amoebae), also extracellular Ca2+ and Mg2+ are potent inducers of these cells' chemotaxis, and the amoebae of D. discoideum can respond to various chemoattractants differently. In the positively developing gradients of folic acid, cAMP, Ca2+, and Mg2+ oriented locomotion of amoebae directed towards the higher concentration of the tested chemoattractants was observed. However, in the negatively developing (temporal) and stationary linear (spatial) gradients, the univocal chemotaxis of amoebae was recorded only in the case of the Mg2+ concentration gradient. This demonstrates that amoebae can respond to both developing and stationary gradients, depending upon the nature of the chemoattractant. We also investigated the effects of chosen inhibitors of signalling pathways upon chemotaxis of D. discoideum amoebae in the positively developing (temporal) gradients of tested chemoattractants. Verapamil was found to abolish the chemotaxis of amoebae only in the Ca2+ gradients. Pertussis toxin suppressed the chemotactic response of cells in the gradients of folic acid and cAMP but did not prevent chemotaxis in those of Ca2+ and Mg2+, while quinacrine inhibited chemotaxis in the gradients of folic acid, cAMP, and Ca2+ but only slightly affected chemotaxis in the Mg2+ gradient. None of the tested inhibitors causes inhibition of cell random movement, when applied in isotropic solution. Also EDTA and EGTA up to 50 mM concentration did not inhibit locomotion of amoebae in control isotropic solutions. Cell Motil. Cytoskeleton 53:1–25, 2002.

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