Calcium regulation of flagellation in Naegleria gruberi

The amoeba-to-flagellate transformation of Naegleria gruberi was studied, exploring the role of calcium in control of this pattern of morphogenesis. A direct and an indirect role for calcium are postulated based on experimental results. Direct inhibition in the presence of calcium is caused by ionophore A23187, substances with ionophore-like activity (amphotericin) and the hormone calcitonin, which facilitate calcium uptake into the cytosol. The indirect role is difficult to assess, but is believed to be related to calcium regulatory protein and its control of cyclic nucleotide levels in the cell, based on inhibition by trifluoperazine. Calcium flux was studied by addition of 45Ca2+ to cell cultures, and tracing its movement during the transformation period. Ultrastructural localization of calcium was attempted in amoeboid and flagellate stages, as well as in reverting flagellates. Deposits that might represent calcium were observed under the plasma membrane and, in calcium-induced reversion, in electron-dense spheres seen in the cytoplasm and at sub-membrane locations, suggesting expulsion of excess calcium.