Effects of enhanced extracellular ammonia concentration on cultured mammalian retinal glial (müller) cells

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Abstract
Müller (glial) cells of the neonatal rabbit retina were cultured as confluent monolayers and exposed to enhanced concentrations of ammonia (0.25, 0.5, 1, 3, 7, and IC mM) in medium for various periods (30 min to 10 d). This caused, in a time‐ and dose‐dependent manner, similar changes in the Müller cells as had previously been described in cultured astrocytes. The most conspicuous events were (1) an increasing size of cell nuclei, (2) an accumulation of phagocytotic vacuoles, and (3) a rearrangement of intermediate filaments. (4) A considerable number of cells died when higher ammonia concentrations were applied for more than 1 h. Simultaneous application of dibutyrylcyclic adenosine monophosphate (dBcAMP) prevented almost completely both the increase in cell nucleus size and the changes of intermediate filaments, but only partly the early cell death of a subpopulation of cells, and the accumulation of phagocytotic vacuoles. Further changes evoked by enhanced ammonia concentration were (5) an accumulation of lipofuscin‐like material (“fatty degeneration”) revealed by lipophilic stain, (6) reduced immunoreactivity for cathepsin D, and increased immunoreactivity for (7) glial fibrillary acidic protein, (8) glutamine synthetase, and (9) bcl‐2 protooncogene protein. These findings are discussed in respect to the possible underlying pathophysiological mechanisms.