Role of glial K+ channels in ontogeny and gliosis: A hypothesis based upon studies on Müller cells
✍ Scribed by Andreas Bringmann; Mike Francke; Thomas Pannicke; Bernd Biedermann; Hannes Kodal; Frank Faude; Winfried Reichelt; Andreas Reichenbach
- Publisher
- John Wiley and Sons
- Year
- 2000
- Tongue
- English
- Weight
- 188 KB
- Volume
- 29
- Category
- Article
- ISSN
- 0894-1491
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✦ Synopsis
The electrophysiological properties of Mu ¨ller cells, the principal glial cells of the retina, are determined by several types of K ϩ conductances. Both the absolute and the relative activities of the individual types of K ϩ channels undergo important changes in the course of ontogenetic development and during gliosis. Although immature Mu ¨ller cells express inwardly rectifying K ϩ (K IR ) currents at a very low density, the membrane of normal mature Mu ¨ller cells is predominated by the K IR conductance. The K IR channels mediate spatial buffering K ϩ currents and maintain a stable hyperpolarized membrane potential necessary for various glial-neuronal interactions. During ''conservative'' (i.e., non-proliferative) reactive gliosis, the K IR conductance of Mu ¨ller cells is moderately reduced and the cell membrane is slightly depolarized; however, when gliotic Mu ¨ller cells become proliferative, their K IR conductances are dramatically down-regulated; this is accompanied by an increased activity of Ca 2ϩ -activated K ϩ channels and by a conspicuous unstability of their membrane potential. The resultant variations of the membrane potential may increase the activity of depolarizationactivated K ϩ , Na ϩ and Ca 2ϩ channels. It is concluded that in respect to their K ϩ current pattern, mature Mu ¨ller cells pass through a process of dedifferentiation before proliferative activity is initiated.