A calcium-dependent mechanism for synapse and nerve cell membrane modulation.

A theory is presented according to which the neuronal membrane and synapses are influenced by membrane-bound S100 protein and a membrane-associated network of actin-like, 20-A-diameter, coiled filaments and the competition by both proteins for Ca(2+). The discussion is based on observations made with fluorescein- and peroxidase-conjugated antiserum against S100 protein on isolated nerve cells. A small part of the S100 protein is membrane-bound in a polar localization that develops postnatally. The competition for Ca(2+) can influence the state of the network filaments which uncoil on binding Ca(2+) and affect differently the conformational state of synapses and membrane depending on the S100 protein content.