The effect of S100 protein on the plasma membrane function of neurons

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Abstract
The protein S100 markedly increases the net intake of GABA across the plasma membranes of Deiters' neurons which have GABA receptors on their surfaces. This membrane function of S100 was found by using a new microtechnique. Plasma membranes of such cells have been freshly prepared by freehand microsurgery and are tightly fixed over a 30-µm ø hole between two compartments of a microchamber containing 2.0 mM GABA in 7.5 µl and 0.2 mM GABA in 75 µl, respectively. The transport of GABA has been determined after incubation of the membrane for from 30 sec to 10 min at 29°C. GABA is transported at a rate of 145 ng in 3 min over a 700-µm2 membrane area. S100 in its calcium form reacts with the membrane and increases GABA transport by 20% which is ATP dependent and inhibited by ouabain and ruthenium red. The kinetics of the transport furthermore prove that GABA transport across the plasma membrane is an active process.