Studies on the mechanism of cell elongation in Blepharisma japonicum. II. Changes of the membrane potential measured by an electrode sensitive to tetraphenyl phosphonium.

An electrode sensitive to tetraphenyl phosphonium (TPP+) was applied to monitor the changes in the membrane potential of the ciliate Blepharisma japonicum during the process of cell elongation. Uptake of TPP+ by Blepharisma cells was observed when they were incubated in a medium containing 2 x 10(-6)M TPP+. Subsequent light stimulation (3,000 lux) led to an efflux of accumulated TPP+ from the cells, indicating that depolarization of the plasma membrane occurred with the concomitant cell elongation. TPP+ efflux was always observed whenever cell elongation was induced in response to various stimuli: valinomycin (10(-6)M), K+ (30 mM), Co2+ (5 mM), and Ca2+ (5 mM). Furthermore, elongation was also evoked by electrical stimulation. These observations indicate that membrane depolarization is involved in the process of cell elongation in Blepharisma.