Channels for amino acids and metabolites activated by cell volume regulation.

Cell volume regulation after swelling has been widely demonstrated and attributed to a loss of KCl in the external medium. But it was also shown in a few cell types that organic cell osmolytes, particularly amino acids, were contributing to volume regulation. These effluxes occurred through a diffusional type of transport. Electrophysiological experiments with patch-clamp electrodes have demonstrated the activation of selective K+ channels in parallel with chloride channels during volume regulation. These chloride channels appear much less selective for a large variety of anions. Many cell osmolytes, not only negatively charged but also neutral ones, are permeable through these channels. When the cells swell in hypotonic media, they loose amino acids and other neutral and negative osmolytes through these channels. It is possible that these channels in astrocytes play an important role in pathological conditions, e.g. brain ischemia, by releasing glutamate in the external medium and contributing to the damaging effect of glutamate in ischemia.