Nonuniform Distribution of Ca2+ Uptake Sites within Human Neutrophils

Abstract

The rate at which Ca2+ returns towards the basal concentration is controlled by the action of Ca2+ pumps, both on the plasma membrane and on organelles within the cytosol. The distribution of Ca2+ 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 Ca2+ 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 Ca2+ uptake rates a clear nonuniformity of Ca2+ uptake sites throughout the neutrophil cytosol was observed. The location of the Ca2+ uptake sites did not correlate with the granules or the main body of the nucleus, but Ca2+ 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 Ca2+ uptake sites plays a role in restricting Ca2+ signals with the neutrophil cytosol.