Calcium waves and development.

Those calcium oscillations which go deep into cells take the form of 'fast' calcium waves. In fully active cells at room temperature, these move at 15-30 microns/s and are propagated by a reaction-diffusion mechanism governed by the Luther equation in which calcium ions are the only propagators and calcium-induced calcium release is the only reaction. However, they may be initiated by a second mode of Ca(2+)-induced Ca2+ release within the lumen of the endoplasmic reticulum (ER). In sea urchin fertilization, this second mode of Ca(2+)-induced Ca2+ release is in turn begun by calcium entering the sperm and thence the ER. Subsurface calcium waves include an important class of surface contraction waves which move at 0.3-3 microns/s and are called 'slow' waves. Their prototype is the 0.5 micron/s wave which accompanies and controls cytokinesis in large eggs. Slow waves may be propagated by mechanical tension rather than by diffusion. Recent work with Dictyostelium transfected with apoaequorin has provided the first views of free calcium patterns within a developing, multicellular organism. During most or all of development, those regions which will differentiate into stalk or stalk-like cells (as opposed to spores) exhibit frequent calcium pulses. These pulses are believed to be fast calcium waves and to feed back on these regions so as to favour non-spore differentiation.