Specific activities of a membrane protein of brain cells

Evidence is presented that the brain-specific protein S-100 is a constituent of the neuronal plasma membrane. This differentiation of the membrane is dependent on stimuli from the environment. Antiserum raised to S-100 was used in a microchamber to separate isolated nerve cells that had S-100 expressed on the surface. Microbeads covered by antiserum to S-100 were used for localization and for cell separation. The S-100 function was studied by a new technique to test the effect of membrane S-100 protein in its calcium form on transport of gamma-aminobutyric acid (GABA) across freshly prepared nerve cell membranes from Deiters' neurons. Membrane S-100 stimulated such GABA transport up to 40%, which was found by kinetic measurements and other tests to be an active transport system. Glia, as a thin layer covering the nerve cell membrane, inhibit the stimulated GABA transport. The glia regulation of the S-100 protein's activity on the neural plasma membrane is discussed.