Control of glial cell volume in anoxia. In vitro studies on ischemic cell swelling.

Abstract

Volume regulation of C6 glial cells was studied in anoxia in vitro to improve the understanding of ischemic cell swelling in the brain. Contrary to in vivo conditions, anoxia or anoxia plus iodoacetate for additional inhibition of anaerobic energy metabolism did not induce glial swelling. However, intracellular K + was markedly decreased while intracellular Na + increased. Induction of energy failure by anoxia plus iodoacetate was found to prevent the regulatory volume decrease on hyposmotic exposure of the cells, which is regularly observed hi normoxic control conditions. Hyposmotic exposure hi anoxia plus iodoacetate led only to an initial tendency of cell volume normalization followed by secondary cell swelling. This was associated with a net increase of intracellular Na + that may explain the failure of volume regulation under these circumstances. Maintenance of a normal glial cell size during complete energy deprivation by anoxia plus iodoacetate hi isotonic medium strongly indicates that energy failure per se does not suffice to induce cell swelling. Cell swelling hi cerebral ischemia in vivo thus is likely to require additional mechanisms, most likely an Increase of membrane permeability to Na + , which may be caused by release and accumulation of excitotoxins such as glutamate or by an extracellular release of K + . Such a mechanism would hardly influence the extracellular homeostasis in vitro due to the large medium-to-cell volume ratio. The findings demonstrate, nonetheless, the significance of a competent energy metabolism to support cell volume regulation. This is concluded from the failure of regulatory volume decrease of hypotonlcally suspended glial cells hi anoxia plus iodoacetate. The experimental conditions employed appear particularly useful to analyze and to differentiate on a molecular level the complex interactions resulting hi ischemic cell swelling hi the brain. {Stroke 1987;18:623-628) W hen the cerebral circulation is interrupted or decreases below a critical threshold, drastic swelling of dendrites and glial cells ensues. A shift of fluid and Na + from the extracellular to the intracellular space is seen after a latency of only 2-3 minutes.1 " 4 The resulting energy failure is thought to disturb the double Donnan equilibrium, which under physiologic conditions ensures a stable cell volume.5 This interpretation, however, might be too simple. The rapid onset of swelling and the complete breakdown of ion gradients suggest an involvement of additional pathogenetic mechanisms, e.g., release or activation of mediator compounds 6 that promote the development of cytotoxic brain edema by increasing membrane permeability or by inflicting membrane damage.Numerous in vivo studies have been performed to elucidate ischemic cell swelling in the brain. The multitude of parameters changing simultaneously, however, make it difficult to determine the significance of individual factors. Therefore, an in vitro method has been established 7 to study the specific processes causing cell swelling and eventuall...

Ischemia‐induced changes of intracellular water diffusion in rat glioma cell cultures

“…Finally, it is important to note that the experiments described in this communication were carried out in C6 cell cultures and the generality of these results to other cell cultures, to neurons, or to tissue has not been established. C6 cells were employed in these experiments because they are a well‐characterized cell line that retain many glial‐specific properties (24–26, 29) and will fill the extrafiber space in the HFBR to tissue‐like cell densities. This is an important feature for investigating water motion within and between cells.…”

Changes in Extracellular Amino Acids and Spontaneous Neuronal Activity During Ischemia and Extended Reflow in the CA1 of the Rat Hippocampus

“…The postischemic increase in extracellular cysteine sulfinate (Andink et al, 1991) may stimulate the release (Dunlop et al, 1989) or inhibit the uptake of aspartate and glutamate (Iwata et al, 1982). Another possibility is reduced glial uptake of amino acids due to edema (Petito, 1986;Kempski et al, 1987;Torp et al, 1991).…”