THE ROLE OF CALCIUM IN AGGREGATION AND DEVELOPMENT OF DICTYOSTELIUM

Changes in cytosolic Ca2+ play an important role in a wide array of ce ll types and the control of its concentration depends upon the interpl ay of many cellular constituents. Resting cells maintain cytosolic cal cium ([Ca2+](i)) at a low level in the face of steep gradients of extr acellular and sequestered Ca2+. Many different signals can provoke the opening of calcium channels in the plasma membrane or in intracellula r compartments and cause rapid influx of Ca2+ into the cytosol and ele vation of [Ca2+](i). After such stimulation Ca2+ ATPases located in th e plasma membrane and in the membranes of intracellular stores rapidly return [Ca2+](i) to its basal level. Such responses to elevation of [ Ca2+](i) are a part of an important signal transduction mechanism that uses calcium (often via the binding protein calmodulin) to mediate a variety of cellular actions responsive to outside influences.