S100-glia regulation of GABA transport across the nerve cell membrane

Abstract

A technique has been devised to isolate and prepare fresh nerve cell plasma membranes in order to study the transport of biologically active substances across the membrane and in the two opposite directions. The membrane is placed tightly over a 30-micrometer diameter hole in a thin glass plate forming a partition between two compartments of a micro-chamber made from silicon rubber. The plasma membrane is usually placed with the outer surface facing the upper compartment. We have studied the transport of labeled GABA across the plasma membrane of Deiters' nerve cells and the effect of the brain-specific protein S-100 in its calcium form on this process. 100 nl samples were separated by thin layer chromatography and each sample analyzed by an instrument especially made for low level 3H- and 14C-measurements. The S-100, Ca2+ protein significantly increased the GABA transport across the nerve cell membrane by maximally 25% and against a gradient. The kinetics of the transport process, and inhibition by 2-4 diaminobutyric acid, furthermore supported the conclusion that the S-100, Ca2+-stimulated GABA transport was an active process. When a thin layer of the nerve cell's S-100-synthesizing glia was placed in contact with the plasma membrane - as in the vivo situation - the stimulation of GABA transport was abrogated. The S-100, Ca2+ protein, if absorbed on the nerve cell membrane, stimulates GABA transport across the membrane. This phenomenon seems to be regulated by the glia which cover all parts of the plasma membrane except the post-synaptic areas.