Influx of extracellular Ca2+ is necessary for electrotaxis in Dictyostelium.

Intracellular free Ca2+ (Ca2+) is a pivotal signalling element in cell migration and is thought to be required for chemotaxis of Dictyostelium. Ca2+ signalling may also be important for electrotaxis. However this suggestion has been controversial. We show that electric fields direct Dictyostelium cells to migrate cathodally and increase Ca2+ in Dictyostelium cells, as determined by Fluo-3 AM imaging and (45)Ca2+ uptake. Omission of extracellular Ca2+(Ca2+) and incubation with EGTA abolished the electric-field-stimulated Ca2+ rise and directional cell migration. This suggests a requirement for Ca2+ in the electrotactic response. Deletion of iplA, a gene responsible for chemoattractant-induced Ca2+ increase, had only a minor effect on the electric-field-induced Ca2+ rise. Moreover, iplA-null Dictyostelium cells showed the same electrotactic response as wild-type cells. Therefore, iplA-independent Ca2+ influx is necessary for electrotactic cell migration. These results suggest that the Ca2+ regulatory mechanisms induced by electric fields are different from those induced by cAMP and folic acid in Dictyostelium cells. Different roles of the iplA gene in chemoattractant-induced and electrically induced Ca2+ signalling, and different effects of Ca2+ elevation on chemotaxis and electrotaxis indicate that the chemoattractant and electric cues activate distinctive initial signalling elements.