Intracellular free calcium responses during chemotaxis of Dictyostelium cells.
A calcium ion indicator, fura-2 bovine serum albumin, was introduced into Dictyostelium discoideum cells by electroporation. The concentration of intracellular calcium ions ([Ca2+]i) increased transiently in vegetative cells upon stimulation with submicromolar concentrations of folic acid, a chemoattractant for this organism at the vegetative stage. Similar [Ca2+]i responses were also observed in aggregation-competent cells upon stimulation with subnanomolar concentrations of cAMP, a chemoattractant at the aggregation stage. The [Ca2+]i response caused by cAMP was 2.1 times higher than that caused by folic acid. The magnitude of these responses depended on the concentration of Ca2+ in the external buffer. The presence of magnesium ions inhibited the [Ca2+]i responses in a dose-dependent manner. [Ca2+]i was higher in the rear region than in the anterior region of cells freely migrating on the surface, although such a gradient was not always maintained. When aggregation competent cells were locally stimulated by the application of a microcapillary containing cAMP, the cells extended pseudopods toward the microcapillary. In these cases, an increase in [Ca2+]i was transiently observed in the region opposite to the tip of the capillary. At the slug stage, [Ca2+]i was higher in prestalk cells than in prespore cells of slugs. The possibility that the [Ca2+]i is spatially regulated within a cell was discussed.
Yumura
S
S
Department of Biology, Faculty of Science, Yamaguchi University, Japan. yumura@po.cc.yamaguchi-u.ac.jp
Furuya
K
K
Takeuchi
I
I
D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002630:Chemotactic Factors / Q000494:pharmacology*; D002633:Chemotaxis / Q000502:physiology*; D000242:Cyclic AMP / Q000494:pharmacology; D004023:Dictyostelium / Q000187:drug effects / Q000378:metabolism*; D005456:Fluorescent Dyes / Q000737:chemistry; D005492:Folic Acid / Q000494:pharmacology*; D016257:Fura-2 / Q000737:chemistry; D012710:Serum Albumin, Bovine / Q000737:chemistry
D002630:Chemotactic Factors; D005456:Fluorescent Dyes; D012710:Serum Albumin, Bovine; D005492:Folic Acid; D000242:Cyclic AMP; D002118:Calcium; D016257:Fura-2