Calcium wave for cytoplasmic streaming of Physarum polycephalum.

The plasmodium Physarum polycephalum exhibits periodic cycles of cytoplasmic streaming in association with those of contraction and relaxation movement. In the present study, we injected Calcium Green dextran as a fluorescent Ca2+ indicator into the thin-spread living plasmodium. We found changes in the [Ca2+]i (intracellular concentration of Ca2+), which propagated in a wave-like form in its cytoplasm. The Ca2+ waves were also detected when we used Fura dextran which detected [Ca2+]i by the ratio of two wavelengths. We prepared the plasmodial fragment from the thin-spread and found that the cycles of the contraction-relaxation movement was so synchronized that the measurement of its area provided an indication of the movement. We observed that [Ca2+]i also synchronized in the entire fragment and that the relaxation ensued upon the reduction in [Ca2+]i. We suggest that the Ca2+ wave generated periodically is one of the major factors playing a crucial role in the relaxation of P. polycephalum.

Temporal relationship between cytosolic free Ca(2+) and membrane potential during hypotonic turgor regulation in a brackish water Charophyte Lamprothamnium succinctum.

Internodal cells of a brackish water charophyte, Lamprothamnium succinctum, regulate turgor pressure in response to changes in external osmotic pressure by modifying vacuolar concentrations of KCl. An increase in cytosolic concentration of free Ca(2+) ([Ca(2+)](c)) is necessary for the progress of turgor regulation induced by hypotonic treatment. Initial changes in membrane potential and [Ca(2+)](c) upon hypotonic treatment were measured to examine the temporal relationship between the two parameters. Fura-dextran (potassium salt, M(r) 10,000, anionic) that had been injected into the cytosol was used to measure [Ca(2+)](c). Membrane potential and membrane conductance under a current-clamp condition were also measured. Decrease in external osmotic pressure by 0.16 Osm induced a simultaneous increase in [Ca(2+)](c) with both depolarization of the membrane and increase in the membrane conductance. Decrease in external osmotic pressure by 0.05 Osm induced a simultaneous increase in [Ca(2+)](c) with membrane depolarization but the increase in membrane conductance started later than the other two processes. There was a close temporal relationship between the increase in [Ca(2+)](c) and membrane depolarization on the initial response of turgor regulation induced by hypotonic treatment.