CSM News
Electronic Edition
Volume 3, number 15
October 29, 1994

Please submit abstracts of your papers as soon as they have been
accepted for publication by sending them to
CSM-News@worms.cmsbio.nwu.edu.

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===========
 Abstracts
===========

Introduction of calcium buffers into the cytosol of Dictyostelium
discoideum amoebae alters cell morphology and inhibits chemotaxis.

Nicola Unterweger and Christina Schlatterer

Faculty of Biology, University of Konstanz, D-78434 Konstanz, FRG;
e-mail: Christina.Schlatterer@uni-konstanz.de

Cell Calcium, in press.

SUMMARY

   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.

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