Osmotic swelling characteristics of glial cells in the murine hippocampus, cerebellum, and retina in situ

Glial cells are proposed to play a major role in the ionic and osmotic homeostasis in the CNS. Swelling of glial cells contributes to the development of edema in neural tissue under pathological conditions such as trauma and ischemia. In this study, we compared the osmotic swelling characteristics of murine hippocampal astrocytes, cerebellar Bergmann glial cells, and retinal Muller glial cells in acutely isolated tissue slices in response to hypoosmotic stress and pharmacological blockade of Kir channels. Hypoosmotic challenge induced an immediate swelling of somata in the majority of Bergmann glial cells and hippocampal astrocytes investigated, whereas Muller cell bodies displayed a substantial delay in the onset of swelling and hippocampal astroglial processes remained unaffected. Blockade of Kir channels under isoosmotic conditions had no swelling-inducing effect in Muller cell somata but caused a swelling in brain astrocytic somata and processes. Blockade of Kir channels under hypoosmotic conditions induced an immediate and strong swelling in Muller cell somata, but had no cumulative effect to brain astroglial somata. No regulatory volume decrease could be observed in all cell types. The data suggest that Kir channels are differently implicated in cell volume homeostasis of retinal Muller cells and brain astrocytes and that Muller cells and brain astrocytes differ in their osmotic swelling properties.