Glutamate opens Na⁺/K⁺ channels in cultured astrocytes

Abstract

Glial cells from different brain regions and species are depolarized by the neurotransmitter glutamate. The depolarization or, if voltage-clamped at the resting membrane potential, the inward current induced by glutamate could be due either to activation of receptor-coupled ion channels or electrogenic uptake of the transmitter. In the present study we applied the patch-clamp technique in the whole-cell recording mode to analyze glutamate-induced currents in cultured astrocytes from rat cerebral hemispheres. At the resting membrane potential, glutamate induced an inward current ranging from 40 to 300 pA. This current decreased in size with depolarization and reversed at about 0 mV. The resulting current-to-voltage curve was linear and depended strongly on the transmembrane Na+ but not on the Ca++ or Cl- gradient. In the presence of glutamate, current noise increased at potentials positive or negative from the reversal potential indicating that ionic channels are activated by glutamate. Both kainate and quisqualate mimicked the effect of glutamate. We conclude that glutamate opens a Na+/K+ channel in cultured astrocytes because of activation of a receptor which shares many properties with the neuronal kainate/quisqualate receptor.

From the Golgi–Cajal mapping to the transmitter-based characterization of the neuronal networks leading to two modes of brain communication: Wiring and volume transmission

“…Extrasynaptic location of receptors has been observed mainly for G-protein-coupled receptors, but also for ion channel linked receptors . Both these types of receptors have been observed on astroglia which generally lack synapses, giving evidence for neuron-glia communication via VT (see Kimelberg, 1988;Stone and Ariano, 1989;Murphy and Pearce, 1987;Sontheimer et al, 1988;Barres et al, 1990;Aoki, 1992;Azmitia and Whitaker-Azmitia, 1991). These studies emphasize the impact of VT in the information handling of the local circuits.…”

Patching the glia reveals the functional organisation of the brain

“…Electrophysiological recordings from cultured glial cells (Fig. 4); further patch clamp studies characterised functional glutamate and GABA receptors in macroglial cells [17,81]. Within the next decade, a huge variety of neurotransmitter receptors were discovered in cultured glial cells (see [72,[85][86][87] for Bergmann glial cell and its neighbour Purkinje neurone bear a similar set of neurotransmitter receptors.…”

Mechanisms of H+and Na+Changes Induced by Glutamate, Kainate, and d-Aspartate in Rat Hippocampal Astrocytes

“…It was caused, therefore, by influx of Na ϩ through receptor-coupled cation channels (Sontheimer et al, 1988 (Table 1). In addition to receptor-mediated Na ϩ influx, our data suggest that 40 -50% of the Glu-induced [Na ϩ ] i increase was caused by Na ϩ transport via Glu uptake, because it persisted in CNQX (Fig.…”