Involvement of Ca2 + and flowing endoplasm in recovery of cytoplasmic streaming after K+-induced cessation

When K+ of high concentration (50 mM) was applied toNitella cells, the cytoplasmic streaming stopped instantly as in the case of electrical stimulation. Recovery of the streaming after chemical stimulation was much slower than after electrical stimulation. When the endoplasm content was modified by centrifugation, streaming recovery was accelerated in the centrifugal cell fragments rich in endoplasm and deccelerated in those poor in it. The recovery was also accelerated either by permeabilizing the plasmalemma in the presence of EGTA in the external solution or by removing the tonoplast by vacuolar perfusion with the EGTA-containing medium. We concluded that the streaming was recovered due to decrease of the cytoplasmic Ca2+ concentration, which seems to be accelerated by sequestering of Ca2+ by endoplasmic components. The slow recovery of the streaming after KCl-stimulated cessation is assumed to be caused by continuous influx of Ca2 + during the prolonged membrane depolarization.