Nonuniform distribution of Ca(2+) uptake sites within human neutrophils

The rate at which Ca(2+) returns towards the basal concentration is controlled by the action of Ca(2+) pumps, both on the plasma membrane and on organelles within the cytosol. The distribution of Ca(2+) uptake sites within the cytosol was investigated using rapid confocal imaging (55 ms/frame) of fluo3-loaded human neutrophils. In some zones within the cell, the uptake of Ca(2+) from the cytosol followed a single exponential time course, whereas in others, there was accelerated kinetics after about 3 s. Using the full array of data, to produce a cell-map of Ca(2+) uptake rates a clear nonuniformity of Ca(2+) uptake sites throughout the neutrophil cytosol was observed. The location of the Ca(2+) uptake sites did not correlate with the granules or the main body of the nucleus, but Ca(2+) uptake was highest near the vestigial Golgi/ER, the edges of the nuclear lobes and at the leading cell edge. The possibility exists that the nonuniform distribution of Ca(2+) uptake sites plays a role in restricting Ca(2+) signals with the neutrophil cytosol.