High-salt solutions prevent reactivation of euglenoid movement in detergent-treated cell models ofEuglena gracilis

Summary Detergent-treated cell models ofEuglena gracilis showed rounded-up movement of the cell body upon addition of ATP and Ca²⁺. Reactivation of the cell models was inhibited when the cell models had been treated with solutions containing >150 mM NaCl or >300 mM KC1. When the supernatant of salt-extracted cell models was subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, two distinctive bands of 120 and 160 kDa were found to be enriched. The cell membrane and associated cytoskeleton (pellicular complex) were isolated after treatment with salt solutions, and examined by electron microscopy to identify essential cortical structures required for reactivating rounding-up cell movement. Among three regularly arranged microtubules, only one and its associated structures were selectively dissolved from the pellicular strips, while the other pellicular elements remained intact. These structures were located in the groove region where sliding between strips is believed to occur during cell shape change. These results suggest a possible involvement of microtubule 2 and its associated bridges in active sliding between adjacent pellicular strips during euglenoid movement.