Presynaptic Glycine Receptors Influence Plasma Membrane Potential and Glutamate Release

Glycine is a classical inhibitory neurotransmitter however presynaptic glycine receptors have rather depolarizing action. Reasons for latter phenomenon are unknown. In the present paper we have investigated how glycine influences cytosolic chloride level monitored by fluorescent dye SPQ, membrane potential monitored by fluorescent dye DiSC3(5) and [¹⁴C]-glutamate release in synaptosomes. We estimated that cytosolic chloride concentration in synaptosomes was about 52 ± 1 mM. Glycine (1 mM) induced chloride efflux and caused slow plasma membrane depolarization. Chloride efflux was almost completely blocked by 100 μM strychnine whilst glycine-induced depolarization was only partially. We also showed that 1 mM glycine induced [¹⁴C]-glutamate release via a strychnine-insensitive pathway. Hence we have concluded that glycine was able to induce two independent effects in synaptosomes: (1) Chloride efflux with following depolarization. This efflux was sensitive to strychnine and thereby is probably conducted through glycine-gated ion channels. (2) Glutamate release seems to be mediated by glycine transporters.