Studies on the mechanism of cell elongation in Blepharisma japonicum: 3. Cytoplasmic calcium ions may correlate to cell elongation in calmodulin-dependent manner

Abstract

Among many heterotrichous ciliates, Blepharisma japonicum especially demonstrates negative phototaxis in response to light stimulation, which is attributed to be caused by swimming acceleration accompanied by cell elongation and ciliary reversal. When Blepharisma cells were treated with 0.1 mM EGTA, cell elongation gradually decreased in its degree as the adaptation time lapsed. Calmodulin inhibitors such as W-7 (10(-5) M) and chlorpromazine (10(-5) M) inhibited cell elongation. These results suggest that a rise in cytoplasmic free Ca(2+) concentration might cause cell elongation through the Ca-calmodulin system. On the other hand, Ca(2+)-channel blockers (La(3+), Co(2+), Cd(2+), Zn(2+), Mn(2+) and verapamil) did not inhibit cell elongation. Ca2+ localization examined by calcium pyroantimonate cytochemistry suggests that Ca(2+) ions required for cell elongation might be supplied from the vacuoles located in the cortical region of the cell instead of Ca(2+) influx from the surrounding medium.