Clark, Beverley Anne; (1993) Membrane properties of astrocytes in the rabbit retina. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Until recently, astrocytes were believed to have passive electrical properties, their membranes being exclusively permeable to potassium. Their major roles were thought to be supportive, in particular regulating the neuronal environment by buffering changes in the potassium concentration in the extracellular space that occur during neuronal activity. In the last few years evidence has accrued showing that astrocytes in culture express a variety of both voltage- and ligand-gated channels. It has been suggested that these channels may be involved in astrocyte function and play a role in glial-neuronal interactions in vivo. However, very little work has been carried out to determine the properties of astrocytes in situ. Both cultured and dissociated cells can show vast differences in both their morphological and electrical properties when compared with the same cell-type in vivo. It is important, therefore, to investigate the properties of astrocytes under more physiological conditions. This thesis describes experiments carried out on a whole-mount preparation of the acutely isolated rabbit retina in which the cellular organisation remains intact. Astrocytes on the vitreal surface of this preparation are readily accessible to patch-clamp electrodes. Retinal astrocytes were immunologically identified by their expression of glial fibrillary acidic protein and the whole cell patch-clamp technique used to define their membrane properties. The results show that astrocytes in situ have a resting potential that is set by potassium and that they express voltage-dependent sodium, potassium and calcium currents and non-NMDA type glutamate- and GABA-gated currents. The channel properties of retinal astrocytes are compared and contrasted with similar types of channel found in retinal neurons and those described in previous studies of glial cells. Recent work has shown that some glial cells express non-NMDA type glutamate-gated channels that are permeable to calcium, a property traditionally associated with NMDA receptor channels. Results presented here show that non- NMDA glutamate-gated channels in retinal astrocytes are also permeable to calcium but show different permeability characteristics.

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