title: Introduction of calcium buffers into the cytosol of Dictyostelium discoideum amoebae alters cell morphology and inhibits chemotaxis.
abstract: Differentiating Dictyostelium discoideum amoebae respond chemotactically towards the attractant cAMP. To test whether chemotaxis requires the establishment of a spatial gradient of the cytosolic calcium concentration ([Ca2+]i) we scrape-loaded calcium chelating agents with different affinities for Ca2+ into the cytosol of the cells. The buffers were 1,2-bis(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA) and its derivatives. Parameters analyzed were general cell morphology and the capability to protrude pseudopods and to migrate towards a cAMP-filled capillary. The chelators dose- and time-dependently inhibited spreading of the amoebae on the substrate. Both oriented pseudopod formation and locomotion of the cells were reduced. This effect was overcome by extracellular Ca2+, but not Mg2+. The effects of BAPTA derivatives were compared to the inhibition by BAPTA. A dose-response curve was obtained; 5,5'-difluoro-BAPTA was the most potent analogue. We conclude that a [Ca2+]i-gradient is necessary for orientation and locomotion. Chemotaxis experiments performed in the presence of extracellular EGTA revealed that liberation of Ca2+ from intracellular stores is sufficient for pseudopod formation; yet under physiological conditions influx of extracellular Ca2+ is also used to establish the gradient.
authors.affiliation: Faculty of Biology, University of Konstanz, Germany.
authors.forename: N
authors.initials: N
authors.lastname: Unterweger
authors.forename: C
authors.initials: C
authors.lastname: Schlatterer
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002451:Cell Compartmentation; D002454:Cell Differentiation; D002633:Chemotaxis / Q000502:physiology*; D003600:Cytosol / Q000502:physiology; D004023:Dictyostelium / Q000166:cytology / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000031:analogs & derivatives*; D011554:Pseudopodia / Q000502:physiology; D013997:Time Factors
chemical_list: D004533:Egtazic Acid; D002118:Calcium