Multiple conductance channels in type-2 cerebellar astrocytes activated by excitatory amino acids

Abstract

L-GLUTAMATE and L-aspartate are thought to have a widespread function as synaptic transmitters in the mammalian central nervous system and there are at least three types of neuronal glutamate receptors, which can be activated by the selective agonists N-methyl-D-aspartate (NMDA), quisqualate and kainate. Recent experiments indicate that glutamate receptors also occur in astrocytes. We have used patch-clamp methods to determine whether one type of macroglial cell, the type-2 astrocyte, possesses glutamate receptors, as previously proposed from neurochemical studies. We find that glutamate and related amino acids can evoke whole-cell and single-channel currents in type-2 astrocytes from rat cerebellum. Although these cells are found mainly in white matter, where neurotransmission does not occur, their processes are closely associated with axons at nodes of Ranvier, suggesting that such receptors are involved in neuronal-glial signalling at the node. Our experiments show that glial cells possess quisqualate- and kainate-receptor channels but lack receptors for NMDA. Interestingly, these glutamate channels exhibit multiple conductance levels that are similar in amplitude to the neuronal glutamate channels.

Activation of glutamate receptors and glutamate uptake in identified macroglial cells in rat cerebellar cultures.

“…From our experiments it appears that glutamate receptors are present both in cerebellar type-2 astrocytes (Usowicz et al 1989), and in the 0-2A progenitor cells (from cerebellum and optic nerve) that give rise to type-2 astrocytes, although they are absent from oligodendrocytes which are also derived from the same lineage (see also Cull-Candy et al 1989). It therefore seems that these glutamate receptors cease to be expressed if the 0-2A progenitor differentiates into an oligodendrocyte rather than a type-2 astrocyte.…”

“…It was therefore of interest to investigate whether type-2 astrocytes possessed glutamate receptors in their processes and at their extremities. From earlier work, it was clear that receptors were present in patches removed from the cell soma (Usowicz et al 1989). In the present experiments the distribution of glutamate receptors in type-2 astrocytes was mapped with ionophoretic pipettes containing quisqualate or kainate.…”

“…Recent electrophysiological experiments have indicated that glutamate receptors can occur in cortical astrocytes (Sontheimer, Kettenmann, Backus & Schachner, 1988) and the presence of glutamate receptors in cerebellar type-2 astrocytes has been proposed from neurochemical studies (Gallo, Giovannini, Suergiu & Levi, 1989). Furthermore, patch-clamp recording has demonstrated directly that, in cerebellar type-2 astrocytes, glutamate and related amino acids can evoke whole-cell and single-channel currents (Usowicz, Gallo & Cull-Candy, 1989).…”

Organic electronics for precise delivery of neurotransmitters to modulate mammalian sensory function

“…Astrocytes, a sub-type of glial cells present in the CNS, express the receptor for Glu. Upon binding of Glu, membrane-bound ion channels open immediately, promoting Ca 2+ influx [27][28][29] . Therefore, astrocytes represent an ideal system to monitor Glu activation of cells using real-time single-cell ratiometric Ca 2+ imaging.…”

Proceedings of the Physiological Society, 21‐22 July 1989, Cambridge Meeting: Poster Communications

“…In vivo the oligodendrocytes myelinate axons, while type-2 astrocytes extend endfeet to the nodes of Ranvier (see Miller et al 1989). Type-2 astrocytes possess glutamatereceptor channels (Usowicz et al 1989), and for these receptors to have a functional significance in vivo (i.e. to be able to detect release of glutamate) they might be expected to occur in processes of the type-2 astrocytes and in the migratory 0-2A cell.…”